Add a copied flag to virtual frame elements that tells if a copy has...

Add a copied flag to virtual frame elements that tells if a copy has
been made of the element.  Set it when copying an element, clear it
when writing to an element marked copied and discovering that it is
not copied.

The copied flags on entry frames are exact.  Preparing a frame for
merging set the copied flags to be exact (to increase the likelihood
of matching the entry frame or another frame).

Committed: http://code.google.com/p/v8/source/detail?r=1546

[William Hesse, 2009-03-19 11:50:20]

LGTM.