conts, handlers, and liveness

[Stephen Weeks]

> Now that I'm a little more familiar with the backend, I see that I'm
> really duplicating information.  We can get by with just the jumpInfo
> returning the various liveBegin lists and contInfo and handlerInfo just
> having size information.  That seems a little cleaner.

liveOffsets in the contInfo makes sense to me.  After all, it is only defined if
the jump is a cont.  Maybe a better way to go would be to have a single
property, jumpInfo, that has an option for the handler and an option for the
cont?