pmap and pstack should do a better of making it clear that they are not supported on Mac OS X

pmap and pstack are not supported on Mac OS X.

pstack will give the message "Not available on Darwin". Although the darwin kernel might be the technical reason why it doesn't work, it would be better to the end user to clarify that it is not supported on "Mac OS X" rather than Darwin.

pmap simply produces no output, not even an error message. I looked into this a bit. We are getting into PMap.run(), but it appears the call to CDebugger.getLoadObjectList() is returning an empty list, so nothing is output. We should add an extra check and println here that calls out that pmap is not supported on Mac OS X.

The ClhsdbPMap and ClhsdbPStack tests should also be fixed to attempt to run on Mac OS X and check for the appropriate error messages. Right now they are excluded from running on Mac OS X. The reason I initially started looking into the Mac OS X support for these two tools is because these two tests were excluded on OSX, and I was curious as to why so I experimented with enabling them to see the result.