- allocate numbers in half-size cells, for an 0.5% SunSpider speedup
        http://bugs.webkit.org/show_bug.cgi?id=15772
        
        We do this by using a single mark bit per two number cells, and
        tweaking marking.
        
        Besides being an 0.5% win overall, this is a 7.1% win on morph.

        * kjs/collector.cpp:
        (KJS::):
        (KJS::Collector::heapAllocate):
        (KJS::Collector::markStackObjectsConservatively):
        (KJS::Collector::sweep):
        * kjs/collector.h:
        (KJS::SmallCollectorCell::):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@27292 268f45cc-cd09-0410-ab3c-d52691b4dbfc