This is a backport of code from MySQL 6.0 with cleanups and extensions

The following new options are supported
configure options:
  --with-libevent                  ; Enable use of libevent, which is needed for pool of threads

mysqld options:
--thread-handling=pool-of-threads  ; Use a pool of threads to handle queries
--thread-pool-size=#               ; Define how many threads should be created to handle all queries
--extra-port=#                     ; Extra tcp port that uses the old one-thread-per-connection method
--extra-max-connections=#          ; Number of connections to accept to 'extra-port'
--test-ignore-wrong-options        ; Ignore setting an enum value to a wrong option (for mysql-test-run)



BUILD/SETUP.sh:
  Added libevents (and thus pool-of-threads) to max builds
CMakeLists.txt:
  Added libevent
Makefile.am:
  Added libevents
config/ac-macros/libevent.m4:
  Libevent code for configure
config/ac-macros/libevent_configure.m4:
  Libevent code for configure
configure.in:
  Added libevents
dbug/dbug.c:
  Added _db_is_pushed(); Needed for pool-of-threads code
extra/Makefile.am:
  Added libevents
extra/libevent:
  Libevent initial code
extra/libevent/CMakeLists.txt:
  Libevent initial code
extra/libevent/Makefile.am:
  Libevent initial code
extra/libevent/README:
  Libevent initial code
extra/libevent/WIN32-Code:
  Libevent initial code
extra/libevent/WIN32-Code/config.h:
  Libevent initial code
extra/libevent/WIN32-Code/misc.c:
  Libevent initial code
extra/libevent/WIN32-Code/misc.h:
  Libevent initial code
extra/libevent/WIN32-Code/tree.h:
  Libevent initial code
extra/libevent/WIN32-Code/win32.c:
  Libevent initial code
extra/libevent/buffer.c:
  Libevent initial code
extra/libevent/compat:
  Libevent initial code
extra/libevent/compat/sys:
  Libevent initial code
extra/libevent/compat/sys/_time.h:
  Libevent initial code
extra/libevent/compat/sys/queue.h:
  Libevent initial code
extra/libevent/compat/sys/tree.h:
  Libevent initial code
extra/libevent/devpoll.c:
  Libevent initial code
extra/libevent/epoll.c:
  Libevent initial code
extra/libevent/epoll_sub.c:
  Libevent initial code
extra/libevent/evbuffer.c:
  Libevent initial code
extra/libevent/evdns.c:
  Libevent initial code
extra/libevent/evdns.h:
  Libevent initial code
extra/libevent/event-config.h:
  Libevent initial code
extra/libevent/event-internal.h:
  Libevent initial code
extra/libevent/event.c:
  Libevent initial code
extra/libevent/event.h:
  Libevent initial code
extra/libevent/event_tagging.c:
  Libevent initial code
extra/libevent/evhttp.h:
  Libevent initial code
extra/libevent/evport.c:
  Libevent initial code
extra/libevent/evrpc-internal.h:
  Libevent initial code
extra/libevent/evrpc.c:
  Libevent initial code
extra/libevent/evrpc.h:
  Libevent initial code
extra/libevent/evsignal.h:
  Libevent initial code
extra/libevent/evutil.c:
  Libevent initial code
extra/libevent/evutil.h:
  Libevent initial code
extra/libevent/http-internal.h:
  Libevent initial code
extra/libevent/http.c:
  Libevent initial code
extra/libevent/kqueue.c:
  Libevent initial code
extra/libevent/log.c:
  Libevent initial code
extra/libevent/log.h:
  Libevent initial code
extra/libevent/min_heap.h:
  Libevent initial code
extra/libevent/poll.c:
  Libevent initial code
extra/libevent/select.c:
  Libevent initial code
extra/libevent/signal.c:
  Libevent initial code
extra/libevent/strlcpy-internal.h:
  Libevent initial code
extra/libevent/strlcpy.c:
  Libevent initial code
include/config-win.h:
  Libevent support
include/my_dbug.h:
  ADded _db_is_pushed
include/mysql.h.pp:
  Update to handle new prototypes
include/typelib.h:
  Split find_type_or_exit() into two functions
include/violite.h:
  Added vio_is_pending()
libmysqld/Makefile.am:
  Added libevent
mysql-test/include/have_pool_of_threads.inc:
  Added test for pool-of-threads
mysql-test/mysql-test-run.pl:
  Don't abort based on time and don't retry test cases when run under --gdb or --debug
mysql-test/r/crash_commit_before.result:
  USE GLOBAL for debug variable
mysql-test/r/have_pool_of_threads.require:
  Added test for pool-of-threads
mysql-test/r/pool_of_threads.result:
  Added test for pool-of-threads
mysql-test/r/subselect_debug.result:
  USE GLOBAL for debug variable
mysql-test/t/crash_commit_before.test:
  USE GLOBAL for debug variable
mysql-test/t/merge-big.test:
  USE GLOBAL for debug variable
mysql-test/t/pool_of_threads-master.opt:
  Added test for pool-of-threads
mysql-test/t/pool_of_threads.test:
  Added test for pool-of-threads
mysys/typelib.c:
  Split find_type_or_exit() into find_type_with_warning()
sql/Makefile.am:
  Added libevent
sql/handler.cc:
  Indentation fix.
  Fixed memory loss bug
  Fixed crash on exit when handler plugin failed
sql/mysql_priv.h:
  Added extra_max_connections and mysqld_extra_port
  Added extern functions from sql_connect.cc
sql/mysqld.cc:
  Added support for new mysqld options
  Added code for 'extra-port' and 'extra-max-connections'
  Split some functions into smaller pieces to be able to reuse code
  Added code for test-ignore-wrong-options
sql/scheduler.cc:
  Updated schduler code from MySQL 6.0
sql/scheduler.h:
  Updated schduler code from MySQL 6.0
sql/set_var.cc:
  Added support for changing "extra_max_connections"
sql/sql_class.cc:
  Iniitalize thread schduler options in THD
sql/sql_class.h:
  Added to extra_port and scheduler to 'THD'
sql/sql_connect.cc:
  Use thd->schduler to check number of connections and terminate connection
  Made some local functions global (for scheduler.cc)
vio/viosocket.c:
  Added 'vio_pending', needed for scheduler..c