Allow variable proxies for the same global variable to share the same...

Allow variable proxies for the same global variable to share the same
variable object.

Add a map from names to variables for global scopes just like
non-global scopes.  Variables are added to the map by the parser when
it encounters a declaration in a global scope or else at scope
resolution time by a failed variable lookup from the global scope or
an inner one and with no intervening with statements or possible calls
to eval.

Committed: http://code.google.com/p/v8/source/detail?r=2369

[Kasper Lund, 2009-07-07 09:10:08]

LGTM.