Fixed the following bug:

	Radar 2890573 - JavaScriptCore needs to be thread-safe

	Actually this is only a weak form of thread-safety - you can safely
	use different interpreters from different threads at the same
	time. If you try to use a single interpreter object from multiple
	threads, you need to provide your own locking.

	* kjs/collector.h, kjs/collector.cpp:
	(Collector::lock, Collector::unlock): Trivial implementation of a
	recursive mutex.
	(Collector::allocate): Lock around the body of this function.
	(Collector::collect): Likewise.
	(Collector::finalCheck): Likewise.
	(Collector::numInterpreters): Likewise.
	(Collector::numGCNotAllowedObjects): Likewise.
	(Collector::numReferencedObjects): Likewise.
	* kjs/internal.cpp:
	(Parser::parse): use a mutex to lock around the whole parse, since
	it uses a bunch of global state.
	(InterpreterImp::InterpreterImp): Grab the Collector lock here,
	both the mutually exclude calls to the body of this function, and
	to protect the s_hook static member which the collector pokes at.
	(InterpreterImp::clear): Likewise.
	* kjs/ustring.cpp:
	(statBufferKeyCleanup, statBufferKeyInit, UString::ascii): Convert
	use of static variable
	* kjs/value.cpp:
	(ValueImp::ValueImp, ValueImp::mark, ValueImp::marked,
	ValueImp::setGcAllowed): Grab the GC lock around any flag changes.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@1126 268f45cc-cd09-0410-ab3c-d52691b4dbfc