- Fixed <rdar://problem/4448098> Switch PropertyMap deleted entry 
        placeholder to -1 from UString::Rep::null

        This turned out to be only a small speedup (.12%). That's within the 
        margin of error for super accurate JS iBench, but Shark confirms the 
        same, so I think it's worth landing.

        FYI, I also confirmed that the single entry optimization in 
        PropertyMap is a 3.2% speedup.

        * kjs/property_map.cpp:
        (KJS::PropertyMap::~PropertyMap):
        (KJS::PropertyMap::clear):
        (KJS::PropertyMap::put):
        (KJS::PropertyMap::insert):
        (KJS::PropertyMap::rehash):
        (KJS::PropertyMap::remove):
        (KJS::PropertyMap::addSparseArrayPropertiesToReferenceList):
        (KJS::PropertyMap::checkConsistency):
        * kjs/property_map.h:
        (KJS::PropertyMap::deletedSentinel):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@13066 268f45cc-cd09-0410-ab3c-d52691b4dbfc