re PR libgcj/14751 ([win32] thread creation leaks system handle resources)

	PR libgcj/14751
	* win32-threads.cc (_Jv_ThreadInitData): Zero out thread
	handle in newly-allocated _Jv_Thread_t.
	(_Jv_ThreadDestroyData): Close thread handle.
	(_Jv_ThreadStart): Remove obsolete comment.
	Store handle of newly-created thread in _Jv_Thread_t.
	* include/win32-threads.h: #define WIN32_LEAN_AND_MEAN
	before including <windows.h>
	#define _Jv_HaveCondDestroy

From-SVN: r87362