Consolidate static identifier initializers within CommonIdentifiers.

        No reliably measurable change on SunSpider; maybe a tiny improvement (within 0.2%).

        * kjs/CommonIdentifiers.h: Added static identifiers that were lazily initialized
        throughout the code.

        * kjs/date_object.cpp:
        (KJS::DateObjectImp::DateObjectImp):
        * kjs/function_object.cpp:
        (KJS::FunctionPrototype::FunctionPrototype):
        * kjs/object_object.cpp:
        (KJS::ObjectPrototype::ObjectPrototype):
        * kjs/regexp_object.cpp:
        (KJS::RegExpPrototype::RegExpPrototype):
        Use the values from CommonIdentifiers. 

        * kjs/lookup.h: Caching the identifier in a static wasn't a win on SunSpider, removed it.

        * kjs/value.h:
        (KJS::jsNaN): We already have a shared NaN value, no need for a duplicate here.

        * wtf/MathExtras.h:
        (wtf_atan2): Having local variables for numeric_limits constants is good for readability,
        but there is no reason to keep them static.

        * JavaScriptCore.exp: Don't needlessly export JSGlobalObject::s_head.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@31208 268f45cc-cd09-0410-ab3c-d52691b4dbfc