execution and global memory heap on shutdown.

Added a funcition to get work items from queue without waiting and
additional info when there is no work to do for a extended periods.

page data write.

where trim corrupted the database. Fixed the issue and added temporal 
guards against unalligned write/trim.

and added guard against unalligned trim size.

waiting for a job. They should sleep and let other threads to their work. At
shutdown, we know that we put "work" and that is handled as soon as possible.

Fixed issue on multi-threaded flush at shutdown.
Removed unnecessary startup option innodb_compress_pages.
Added a new startup option innodb_mtflush_threads, default 8.

also on system tables but not per table.

tables.

option using cmake find_library. Fixed bunch of compiler
warnings.

code.

current offset to desired size if posix_fallocate is used.

InnoDB.

where not shut down properly.

Fixed issue on file space extend when posix_fallocate is used.

Merged second iteration of multi-threaded flush code.

Merged page compression feature to XtraDB storage engine.

Added feature where page compression can use lz4 compression
method (innodb_use_lz4, default OFF).

Removed some unnecessary assertions to debug build and enhanced the page_compression and page_compression_level fetch.

Enhancement: Change atomic_writes table option to enum type. Now every file can either use atomic writes, not use it or use default.

SYNTAX: ATOMIC_WRITES=['DEFAULT','ON','OFF']

Idea here is to be able to define innodb_doublewrite = 1 but with following rules:

ATOMIC_WRITES='DEFAULT' - if innodb_use_atomic_writes = 1, we do not write to doublewrite buffer the changes
                          if innodb_use_atomic_writes = 0, we write to doublewrite buffer
ATOMIC_WRITES='ON'      - do not write to doublewrite buffer
ATOMIC_WRITES='OFF'     - write to doublewrite buffer

Note that doublewrite buffer can't be used if innodb_doublewrite = 0.

written and rest of the page is trimmed. In following writes
there is no need to trim again if write_size only increases
because rest of the page is already trimmed. If actual write
size decreases we need to trim again. Need to research if this
can happen frequently enough to make any effect.

Temporal solution: In directFS using atomic writes
we must use posix_fallocate to extend the file because
pwrite past end of file fails but when compression is
used the file pages must be physically initialized with
zeroes, thus after file extend with posix_fallocate
we still write empty pages to file.

Fix all suite.pm files that had errors and test files that were skipped because of that

* remove is_embedded.require

because some suites may be disabled unless a plugin is available,
and compiled-in plugins are only known after collect_mysqld_features().

Additionally move mysql_install_db() after everything else it's collected -
it's a slow process, better do it after all the information is gathered
(and reported to the user).

plugin.cmake does it automatically for all plugins

* rename "xtradb" combination to be called "innodb"
* disable xtradb_plugin embedded tests (because of RECOMPILE_FOR_EMBEDDED)

(it was used only for plugins in mysqld)