Don't show the SymbolicAccessPath results in reports

This change might or might not be temporary.  They are useful
to look at while debugging, but are just noise otherwise.
Improve the precision of the transitive error prop case

See the note in the source, but at a high level this change makes the
analysis smarter about branches that "remove" error codes from return
value sets in the transitive error case.  This requires generating
and checking a few more formulas, but they are small.