Bug#33031 app linked to libmysql.lib crash if run as service in vista under 
localsystem
  

There are some problems using DllMain hook functions on Windows that 
automatically do global and per-thread initialization for libmysqld.dll

1)per-thread initialization(DLL_THREAD_ATTACH)
MySQL internally counts number of active threads that and causes a delay in in 
my_end() if not all threads are exited. But,there are threads that can be 
started either by Windows internally (often in TCP/IP scenarios) or by user 
himself - those threads are not necessarily using libmysql.dll functionality, 
but nonetheless the contribute to the count of open threads.

2)process-initialization (DLL_PROCESS_ATTACH)
my_init() calls WSAStartup that itself loads DLLs and can lead to a deadlock in 
Windows loader.

Fix is to remove dll initialization code from libmysql.dll in general case. I
still leave an environment variable LIBMYSQL_DLLINIT, which if set to any value 
will cause the old behavior (DLL init hooks will be called). This env.variable 
exists only to prevent breakage of existing Windows-only applications that 
don't do mysql_thread_init() and work ok today. Use of LIBMYSQL_DLLINIT is 
discouraged and it will be removed in 6.0