Fix loopjitting

Improve loop arg/ret discovery

Loop-jitting was incorrectly turning local variables into arguments of lifted loop functions when a variable with the same name is used outside of the loop.  This patch improves the overall argument and return value discovery to properly consider the read/write order of variables.  

You are right.  I only need the end of loop offset.  I added the else branch last and didn't rethink the entire logic.