Change ActivationImp to be allocated via the garbage collector

	Change ActivationImp to be allocated via the garbage collector
	again instead of on the stack. This fixes the following four
	regressions but sadly it causes a 6% performance hit. It's
	probably possibly to reduce the hit a bit by being smarter about
	inlining and the way the marking list variant is implemented, but
	I'll look into that later.

	- fixed 3111500 - REGRESSION: crash in "KJS::ScopeChain::mark()" on www.posci.com
	- fixed 3111145 - REGRESSION: reproducible crash in KJS hashtable lookup at time.com
	- fixed 3110897 - REGRESSION: javascript crasher on http://bmwgallery.tripod.com/
	- fixed 3109987 - REGRESSION: Reproducible crash in KJS ObjectImp at live365.com

	Also:

	- improved DEBUG_COLLECTOR mode a bit by never giving memory back
	to the system.

        * kjs/collector.cpp:
        * kjs/context.h:
        * kjs/function.cpp:
        (ActivationImp::ActivationImp):
        (ActivationImp::mark):
        (ActivationImp::createArgumentsObject):
        * kjs/function.h:
        * kjs/internal.cpp:
        (ContextImp::ContextImp):
        (ContextImp::mark):
        * kjs/list.cpp:
        * kjs/list.h:
        * kjs/value.cpp:
        (Value::Value):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@2883 268f45cc-cd09-0410-ab3c-d52691b4dbfc