BUG: #14863 - Fix path initialization when lib dir in parent of .app bundle

This fixes a problem where a "lib" directory was used to determine if
the .app directory is in a build directory.  Use ParaViewConfig.cmake
as a better heuristic (although the same problem would still exist if
that file existed in unexpected places).

Also refactor the if/else statements to be more clear and indicate an error
in the fall-through case that existed previously.

Change-Id: I843ed13409dfc022b2859ffbc41541dde281b1d9
Remove path question comment

I am fairly confident /Contents/Libraries is required on the python path as this is the location of the binary python modules (.so files).  Remove the comment so future developers will not be concerned.

Change-Id: I927a19142992d0bae1c6f64a6cec139dc8969dfd
Merge topic '14863-mac-python-path-fixes' into next

04f78173 Remove path question comment
9f2c9159 BUG: #14863 - Fix path initialization when lib dir in parent of .app bundle