Change the structure of the scavenge collector's loop. Move...

Change the structure of the scavenge collector's loop.  Move
scavenging of objects pointed to by weak handles earlier.  Rename
"mark" => "front" and "top" => "rear" to make it clearer which end is
which.

Committed: http://code.google.com/p/v8/source/detail?r=1900

[Kevin Millikin (Chromium), 2009-05-07 11:37:39]

Because you like reading GC code.

We are still hitting (but skipping) promoted objects when we do IterateRSet. 
That's the next change, but I wanted to keep it separate in case it introduces
flakiness somewhere.

[Erik Corry, 2009-05-07 11:59:21]

LGTM