Backport of this changeset

http://lists.mysql.com/commits/59686

Cleanup pthread_self(), pthread_create(), pthread_join() implementation on Windows.
Prior implementation is was unnecessarily complicated and even differs in embedded
and non-embedded case.
      
Improvements in this patch:
* pthread_t is now the unique thread ID, instead of HANDLE returned by beginthread
      
This simplifies pthread_self() to be just straight GetCurrentThreadId().
prior it was much  art involved in passing the beginthread() handle from the caller
to the TLS structure in the child thread ( did not work for the main thread of
course)
      
* remove MySQL specific my_thread_init()/my_thread_end() from pthread_create.
No automagic is done on Unix on pthread_create(). Having the same on Windows will 
improve portability and avoid extra #ifdef's
      
* remove redefinition of getpid() - it was defined as GetCurrentThreadId()

sql/sql_insert.cc

@@ -2498,7 +2498,6 @@ pthread_handler_t handle_delayed_insert(void *arg)
     since it does not find one in the list.
   */
   pthread_mutex_lock(&di->mutex);
-#if !defined( __WIN__) /* Win32 calls this in pthread_create */
   if (my_thread_init())
   {
     /* Can't use my_error since store_globals has not yet been called */
@@ -2506,13 +2505,9 @@ pthread_handler_t handle_delayed_insert(void *arg)
                                    ER(ER_OUT_OF_RESOURCES), NULL);
     goto end;
   }
-#endif
-
   handle_delayed_insert_impl(thd, di);
 
-#ifndef __WIN__
 end:
-#endif
   /*
     di should be unlinked from the thread handler list and have no active
     clients