Changed behavior of how we handle "NULL" summaries: just call

GRSimpleVals::EvalCal(), and don't change reference counts.

Remove "getDoNothingSummary()", as a NULL summary does the same thing.

Added temporary hack for the "Get" rule for objects that return a pointer type:
treat them as non-owned CF objects.

Added test case to detect the release of a non-owned object.

llvm-svn: 49555