Reviewed by Cameron Zwarich.
        
        - fix for: REGRESSION: over 100 StructureIDs leak loading about:blank (result of fix for bug 21633)
        
        Apparent slight progression (< 0.5%) on v8 benchmarks and SunSpider.

        * kjs/StructureID.cpp:
        (JSC::StructureID::~StructureID): Don't deref this object's parent's pointer to
        itself from the destructor; that doesn't even make sense.
        (JSC::StructureID::addPropertyTransition): Don't refer the single transition;
        the rule is that parent StructureIDs are ref'd but child ones are not. Refing
        the child creates a cycle.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@37632 268f45cc-cd09-0410-ab3c-d52691b4dbfc