Handle PackageMaker a bit better.

Look for the binary in various places, rather than looking for
particular directories and adding them to the path.  That lets us use
the PackageMaker binary from the PackageMaker.app bundle (it can either
be run as a GUI app or from the command line), so you don't have to have
a symlink to it from one of the directories in question.

Change-Id: I1ad701291698544f96d419663f0b4a669876d2f1
Reviewed-on: https://code.wireshark.org/review/5077
Reviewed-by: Guy Harris <guy@alum.mit.edu>