Enable functionality to have multiple background io helper threads.
This patch is based on percona contributions.

More details about this patch will be written at:
https://svn.innodb.com/innobase/MultipleBackgroundThreads

The patch essentially does the following:

expose following knobs:
innodb_read_io_threads = [1 - 64] default 1
innodb_write_io_threads = [1 - 64] default 1

deprecate innodb_file_io_threads (this parameter was relevant only on windows)

Internally it allows multiple segments for read and write IO request arrays
where one thread works on one segement.

Submitted by:	Inaam (rb://124)
Approved by:	Heikki (rb://124)

Fix Mantis Issue#244 fix bug in linear read ahead (no check on access pattern)

The changes are:

1) Take into account access pattern when deciding whether or not to do linear
  read ahead.
2) Expose a knob innodb_read_ahead_factor = [0-64] default (8), dynamic,
  global to control linear read ahead behvior
3) Disable random read ahead. Keep the code for now.

Submitted by:	Inaam (rb://122)
Approved by:	Heikki (rb://122)

  ------------------------------------------------------------------------
  r5150 | vasil | 2009-05-27 18:56:03 +0300 (Wed, 27 May 2009) | 4 lines

  branches/5.1:

  Whitespace fixup.
  ------------------------------------------------------------------------
  r5191 | vasil | 2009-05-30 17:46:05 +0300 (Sat, 30 May 2009) | 19 lines

  branches/5.1:

  Merge a change from MySQL (this fixes the failing innodb_mysql test):

    ------------------------------------------------------------
    revno: 1810.3894.10
    committer: Sergey Glukhov <Sergey.Glukhov@sun.com>
    branch nick: mysql-5.0-bugteam
    timestamp: Tue 2009-05-19 11:32:21 +0500
    message:
      Bug#39793 Foreign keys not constructed when column has a '#' in a comment or default value
      Internal InnoDN FK parser does not recognize '\'' as quotation symbol.
      Suggested fix is to add '\'' symbol check for quotation condition
      (dict_strip_comments() function).
    modified:
      innobase/dict/dict0dict.c
      mysql-test/r/innodb_mysql.result
      mysql-test/t/innodb_mysql.test
  ------------------------------------------------------------------------
  r5233 | marko | 2009-06-03 15:12:44 +0300 (Wed, 03 Jun 2009) | 11 lines

  branches/5.1: Merge the test case from r5232 from branches/5.0:
    ------------------------------------------------------------------------
    r5232 | marko | 2009-06-03 14:31:04 +0300 (Wed, 03 Jun 2009) | 21 lines

    branches/5.0: Merge r3590 from branches/5.1 in order to fix Bug #40565
    (Update Query Results in "1 Row Affected" But Should Be "Zero Rows").

    Also, add a test case for Bug #40565.

    rb://128 approved by Heikki Tuuri
    ------------------------------------------------------------------------
  ------------------------------------------------------------------------

Make the rec parameter of mlog_open_and_write_index() const.

  ------------------------------------------------------------------------
  r5126 | vasil | 2009-05-26 16:57:12 +0300 (Tue, 26 May 2009) | 9 lines

  branches/5.1:

  Preparation for the fix of
  Bug#45097 Hang during recovery, redo logs for doublewrite buffer pages

  Non-functional change: move FSP_* macros from fsp0fsp.h to a new file
  fsp0types.h. This is needed in order to be able to use FSP_EXTENT_SIZE
  in mtr0log.ic.
  ------------------------------------------------------------------------
  r5127 | vasil | 2009-05-26 17:05:43 +0300 (Tue, 26 May 2009) | 9 lines

  branches/5.1:

  Preparation for the fix of
  Bug#45097 Hang during recovery, redo logs for doublewrite buffer pages

  Do not include unnecessary headers mtr0log.h and fut0lst.h in trx0sys.h
  and include fsp0fsp.h just before it is needed. This is needed in order
  to be able to use TRX_SYS_SPACE in mtr0log.ic.
  ------------------------------------------------------------------------
  r5128 | vasil | 2009-05-26 17:26:37 +0300 (Tue, 26 May 2009) | 7 lines

  branches/5.1:

  Fix Bug#45097 Hang during recovery, redo logs for doublewrite buffer pages

  Do not write redo log for the pages in the doublewrite buffer. Also, do not
  make a dummy change to the page because this is not needed.
  ------------------------------------------------------------------------

@defgroup is for source code modules, not for field groups.
Tell Doxygen to expand the UT_LIST declarations.

#defines and global variables.  Many are still missing.

There is nothing for Doxygen to see in this file, move along.

macros and global variables.  Many more to go.

to prevent bogus Doxygen errors.

that is, make Doxygen ignore these test programs.

/*********************************
comments to Doxygen /** style like this:
/*****************************//**

This conversion was performed by the following command:

perl -i -e 'while(<ARGV>){if (m|^/\*{30}\**$|) {
s|\*{4}$|//**| if ++$com>1; $_ .= "\@file $ARGV\n" if $com==2}
print; if(eof){$.=0;undef $com}}' */*[ch] include/univ.i

This is to avoid triggering an error in Doxygen.

This patch was created by running the following commands:

for i in */*[ch]; do doxygenify.pl $i; done
perl -i -pe 's#\*{3} \*/$#****/#' */*[ch]

where doxygenify.pl is
https://svn.innodb.com/svn/misc/trunk/tools/doxygenify.pl r510

Verified the consistency as follows:

(0) not too many /* in: */ or /* out: */ comments left in the code:
grep -l '/\*\s*\(in\|out\)[,:/]' */*[ch]

(1) no difference when ignoring blank lines, after stripping all
C90-style /* comments */, including multi-line ones, before and after
applying this patch:

perl -i -e 'undef $/;while(<ARGV>){s#/\*(.*?)\*/##gs;print}' */*[ch]
diff -I'^\s*$' --exclude .svn -ru TREE1 TREE2

(2) after stripping @return comments and !<, generated a diff and omitted
the hunks where /* out: */ function return comments were removed:

perl -i -e'undef $/;while(<ARGV>){s#!<##g;s#\n\@return\t.*?\*/# \*/#gs;print}'\
 */*[ch]
svn diff|
perl -e 'undef $/;$_=<>;s#\n-\s*/\* out[:,]([^\n]*?)(\n-[^\n]*?)*\*/##gs;print'

Some unintended changes were left.  These will be removed in a
subsequent patch.

Whitespace fixup.

Document the function parameters.

now that the function was declared void in r5060.

srv0start.c does not (any longer) call memcmp.
srv_parse_megabytes(): Add a function comment.