Extending varchar column length with ALTER TABLE may result in unusable
memory table.

The problem is that we use fast ALTER TABLE in this case, which is not
supported by now.

This is fixed by refusing fast ALTER TABLE when extending varchar column.
In other words force copy of a table during ALTER TABLE.

Affects MEMORY tables in 5.1 only.

into  chilla.local:/home/mydev/mysql-5.1-bug25460

Decreased code duplication by calling memory mapping
function through mi_extra().

into  chilla.local:/home/mydev/mysql-5.1-axmrg

into  chilla.local:/home/mydev/mysql-5.1-axmrg

into  chilla.local:/home/mydev/mysql-5.1-axmrg

into  chilla.local:/home/mydev/mysql-5.0-axmrg

into  trift2.:/MySQL/M51/push-5.1

into  zippy.cornsilk.net:/home/cmiller/work/mysql/mysql-5.1-maint

into  zippy.cornsilk.net:/home/cmiller/work/mysql/mysql-5.0-maint

into  chilla.local:/home/mydev/mysql-5.1-axmrg

into  chilla.local:/home/mydev/mysql-5.1-axmrg

into  chilla.local:/home/mydev/mysql-5.0-axmrg

into  chilla.local:/home/mydev/mysql-5.0-axmrg

into  olga.mysql.com:/home/igor/mysql-5.1-opt

into  olga.mysql.com:/home/igor/mysql-5.1-opt

into  bk-internal.mysql.com:/data0/bk/mysql-5.1-opt

into  zippy.cornsilk.net:/home/cmiller/work/mysql/mysql-5.1-maint

into  bk-internal.mysql.com:/data0/bk/mysql-5.0-opt

into  zippy.cornsilk.net:/home/cmiller/work/mysql/bug25807/my51-bug25807

Showstopper and regression against 5.0.24.

Previously, we ignored seek() errors (see Bug#22828) and let seek()s
against pipes fail.  Now, since we check that a seek didn't fail,
and return without reading, this bug popped up.

This restores the behavior for file-ish objects that could never be 
seek()ed.

into  olga.mysql.com:/home/igor/mysql-5.1-opt

into  bk-internal.mysql.com:/data0/bk/mysql-4.1-opt

into  chilla.local:/home/mydev/mysql-5.1-bug25460

into  chilla.local:/home/mydev/mysql-5.1-bug25460-old

into  zippy.cornsilk.net:/home/cmiller/work/mysql/mysql-4.1-maint

into  zippy.cornsilk.net:/home/cmiller/work/mysql/tmpmerge

Under high load it was possible that memory mapping was started on a table
while other threads were working with the table.

I fixed the start of memory mapping so that it is done at the first table
open or when the requesting thread is using the table exclusively only.

  Rename: BitKeeper/deleted/.del-README.txt -> BitKeeper/deleted/.del-README.txt-renamed

into  zippy.cornsilk.net:/home/cmiller/work/mysql/mysql-5.1-maint

into  zippy.cornsilk.net:/home/cmiller/work/mysql/mysql-5.0-maint

into  olga.mysql.com:/home/igor/mysql-5.1-opt

into  pilot.mysql.com:/home/msvensson/mysql/mysql-5.1-new-maint

into  pilot.mysql.com:/home/msvensson/mysql/mysql-5.1-new-maint

into  pilot.mysql.com:/home/msvensson/mysql/mysql-5.0-maint