Cope with cross-deopt-point usage analysis.

If a register gets used after a deopt point, give its usage an extra
bump. This means we won't kill a write to it when doing dead code
elimination. Even if we don't actually read it later in the optimized
code, we still need things set up right for if we deopt. This extra
care will allow us to be a little more aggresive in decrementing usage
in various other situations.
Fix 'elimiante' typo in several places
give ContainerSpec a spesh function, use it for decont.
+ comment, - debug print.
Fix MSVC build.
Make various spesh things available publicly.

Since extops and container specs may participate in spesh also, and so
need some graph manipulation APIs.
Merge remote-tracking branch 'origin/master' into moar-jit