Reviewed by Oliver Hunt.
        
        Fixed <rdar://problem/4681051> Installer crashes in KJS::Collector::
        markOtherThreadConservatively(KJS::Collector::Thread*) trying to install 
        iLife 06 using Rosetta on an Intel Machine
        
        The problem was that our thread-specific data destructor would modify the
        list of active JavaScript threads without holding the JSLock, corrupting
        the list. Corruption was especially likely if one JavaScript thread exited 
        while another was starting up.

        * JavaScriptCore.exp:
        * kjs/JSLock.cpp: Don't conflate locking the JSLock with registering a
        thread, since the thread-specific data destructor needs to lock
        without registering a thread. Instead, treat thread registration as a
        part of the convenience of the JSLock object, and whittle down JSLock::lock()
        to just the bits that actually do the locking.
        (KJS::JSLock::lock):
        (KJS::JSLock::registerThread):
        * kjs/JSLock.h: Updated comments to mention the new behavior above, and
        other recent changes.
        (KJS::JSLock::JSLock):
        * kjs/collector.cpp:
        (KJS::destroyRegisteredThread): Lock here.
        (KJS::Collector::registerThread): To match, assert that we're locked here.

JavaScriptGlue:

        Reviewed by Oliver Hunt.
        
        Updated in light of fix for <rdar://problem/4681051> Installer crashes 
        in KJS::Collector::markOtherThreadConservatively(KJS::Collector::Thread*) 
        trying to install iLife 06 using Rosetta on an Intel Machine
        
        * JavaScriptGlue.cpp:
        (JSLockInterpreter): Ensure backwards compatibility by calling 
        registerThread() when explicitly taking the JSLock. (This doesn't happen 
        automatically anymore.) I doubt this actally matters, but in JavaScriptGlue
        territory, that kind of thinking will get you killed.

WebKitTools:

        Reviewed by Oliver Hunt.
        
        Beefed up --threaded mode in light of <rdar://problem/4681051> Installer 
        crashes in KJS::Collector::markOtherThreadConservatively(KJS::Collector::Thread*) 
        trying to install iLife 06 using Rosetta on an Intel Machine
        
        --threaded mode now runs a bunch of different JavaScript threads, randomly
        killing and respawning them. This was sufficient for reproducing the
        bug on my MacBook Pro.

        * DumpRenderTree/DumpRenderTree.m:
        (javaScriptThreads):
        (runJavaScriptThread):
        (startJavaScriptThreads):
        (stopJavaScriptThreads):
        (dumpRenderTree):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20115 268f45cc-cd09-0410-ab3c-d52691b4dbfc