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)

support ha_innodb.so as a dynamic plugin.
* remove obsolete *,innodb_plugin.rdiff files
* s/--plugin-load=/--plugin-load-add=/
* MYSQL_PLUGIN_IMPORT glob_hostname[]
* use my_error instead of push_warning_printf(ER_DEFAULT)
* don't use tdc_size and tc_size in a module

update test cases (XtraDB is 5.6.14, InnoDB is 5.6.10)
* copy new tests over
* disable some tests for (old) InnoDB
* delete XtraDB tests that no longer apply

small compatibility changes:
* s/HTON_EXTENDED_KEYS/HTON_SUPPORTS_EXTENDED_KEYS/
* revert unnecessary InnoDB changes to make it a bit closer to the upstream

fix XtraDB to compile on Windows (both as a static and a dynamic plugin)

disable XtraDB on Windows (deadlocks) and where no atomic ops are available (e.g. CentOS 5)


storage/innobase/handler/ha_innodb.cc:
  revert few unnecessary changes to make it a bit closer to the original InnoDB
storage/innobase/include/univ.i:
  correct the version to match what it was merged from

modified:
  storage/connect/odbconn.cpp

currently Fusion-io SSD drive does not support setting file
size without fysically writing pages with zeroes when fallocate
with PUCH_HOLE is used.

Added additional error message if atomic write setup does not
succeed.

for Fusion-io currently.

dictionary setting and from there it will be stored to table space.

Fixing "/*100000 ...*/" comments (i.e. MySQL style with 6-digits),
which were unintentionally broken in the MDEV-5009 patch.

modified:
  mysql-test/r/comments.result
  mysql-test/t/comments.test
  sql/sql_lex.cc

tables using atomic write/table.

This is work in progress and some parts are at most POC quality.

modified:
  storage/connect/ha_connect.cc
  storage/connect/myconn.cpp
  storage/connect/odbconn.cpp
  storage/connect/plgdbsem.h

The problem seems to be fixed by some earlier change
and is not reproducible any longer. Only adding a test case.