Experimental: thread live register references to deferred code....

Experimental: thread live register references to deferred code.
Deferred code conceptually appears inline, but it is generated at the
very end of a function.  Since registers could be alive at entry
and/or exit, it needs to know which ones.

We take a snapshot of the global register file's reference counts and
a copy of the virtual frame on entry, and use that to generate the
deferred code.  This requires the register file and frame to match for
deferred code snippets with multiple incoming CFG edges.  That's
trivially true now because all uses of deferred code occur with fully
spilled frames.

Also included are fixes for some small lint issues.

[Kevin Millikin (Chromium), 2008-12-11 16:35:40]

This should enable deferred code safely.  There is still the general issue that
we haven't sorted out what to do with non-frame register references at CFG merge
points.  We should ensure that they are identical on all paths.

[Kevin Millikin (Chromium), 2008-12-17 13:49:35]

I'm closing this issue, because I think we have a better way to do it.