Merge pull request #119 from sbesson/internalretry_unittests

Add unit tests for internal GH API call retries
More robust exception handling in main() entry point

In some conditions we have noticed that not exiting explicitly and
allowing an Exception to bubble up causes the setuptools based command
line scripts to hang.  This commit ensures that the entry point never
allows an exception to bubble up beyond its scope.
merge master -D org -I include -E exclude: PR 120 (More robust exception handling in main() entry point)