Added some missing JSLocks, which might fix <rdar://problem/4889707>.

        We need to lock whenever we might allocate memory because our FastMalloc
        implementation requires clients to register their threads, which we do
        through JSLock. 
        
        We also need to lock whenever modifying ref-counts because they're not 
        thread-safe.

        * API/JSObjectRef.cpp:
        (JSClassCreate): Allocates memory
        (JSClassRetain): Modifies a ref-count
        (JSClassRelease): Modifies a ref-count
        (JSPropertyNameArrayRetain): Modifies a ref-count
        (JSPropertyNameArrayRelease): Modifies a ref-count
        * API/JSStringRef.cpp:
        (JSStringRetain): Modifies a ref-count
        * API/JSValueRef.cpp:
        (JSValueIsInstanceOfConstructor): Might allocate memory if an exception
        is thrown.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@19193 268f45cc-cd09-0410-ab3c-d52691b4dbfc