LiveVariables:

 - Finished 99% of analysis logic.  Probably a few bugs.
 - Added querying functions to query liveness.
 - Added better pretty printing of liveness.
 - Added better bookkeeping of per-variable liveness information.
 - Added LiveVariablesAuditor interface, which allows "lazy" querying
   of intra-basic block liveness information.

Driver:
 - Minor cleanups involved in dumping liveness information.

llvm-svn: 41753