Make it more pleasant to work with expression locations in the...

Make it more pleasant to work with expression locations in the
top-level code generator backend.  Introduce function to move one
location to another (source cannot be nowhere); to move registers,
slots, and literals into a location; and to move a location to a
register or slot.


Committed: http://code.google.com/p/v8/source/detail?r=3146

[fschneider, 2009-10-27 12:51:10]

LGTM.