[boost] [thread] patch for tss.cpp (win32 + static linking support)

Hi, I believe I've found a bug in tss.cpp, for details please ref http://article.gmane.org/gmane.comp.lib.boost.user/26591 . The immediate fix is straightforward, it just involves resetting the native tss value after deleting the pointed-to data at thread exit. Patch is attached to this message. The changes only affects the Win32 platform and I've run the supplied tests under libs/thread/test to verify that it doesn't break anything obvious. As the bug involves dereferencing a dangling pointer and isn't detected most of the time, I'd really appreciate if the patch could be accepted as soon as possible. I'm awaiting Roland Schwartz to "bless" the patch. If he agrees, would it be possible to accept this for 1.34? / Johan