Make storing non-trivial data in wxThreadSpecificInfo possible.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74832 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Make _() and friends safe to call from any thread.

The GetUntranslatedString() hack keeps a global copy of all strings, so
that it can return a const reference as wxGetTranslation() return value.
A global wxHashSet instance shared by all threads won't do, even guarded
with a critical section, because it may internally copy values on any
insert and thus invalidate pointers that may still be used on another
thread.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74833 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Deallocate wxThreadSpecificInfo when wxThread ends.

Cleanup wxThreadSpecificInfo after wxThread::Entry returns to be more
memory efficient.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74834 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Remove unused wxLocale::GetUntranslatedString().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74835 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add wxTranslations::GetTranslatedString().

Replace GetString(), which always returns something (possibly the
original string) with GetTranslatedString() that returns either a
pointer to translated string or NULL.

This simplifies the code a bit, all handling of missing translations is
now done in wxGetTranslation().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74836 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775