Make JavaScriptGlue and JavaScriptCore API functions implicitly call initializeThreading
        for the sake of non-WebKit clients.

JavaScriptCore:
        * API/JSBase.cpp:
        (JSGarbageCollect):
        * API/JSContextRef.cpp:
        (JSGlobalContextCreate):
        These are the JavaScriptCore API bottlenecks. There are a few other JSStringRef
        and JSClassRef functions that can be called earlier, but they do not do anything that
        requires initializeThreading.

        * kjs/InitializeThreading.cpp:
        (KJS::doInitializeThreading):
        (KJS::initializeThreading):
        On Darwin, make the initialization happen under pthread_once, since there is no guarantee
        that non-WebKit clients won't try to call this function re-entrantly.

        * kjs/InitializeThreading.h:
        * wtf/Threading.h:
        Spell out initializeThreading contract.

        * wtf/ThreadingPthreads.cpp: (WTF::isMainThread): Make sure that results are correct on
        Darwin, even if threading was initialized from a secondary thread.

JavaScriptGlue:
        * JavaScriptGlue.cpp:
        (JSRunCreate):
        (JSCollect):
        (JSCreateJSArrayFromCFArray):
        (JSLockInterpreter):
        These are all possible JavaScriptGlue entry points.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@32808 268f45cc-cd09-0410-ab3c-d52691b4dbfc