Imporve error handling

- Don't attempt to continue if we couldn't get current issues (allows
duplicate issues to be created)
- warn if there's a collision due to multiple issues with the same title
Key existing issues by ID instead of title

Parse issue body for ID in URL pointing back to Google Code so that we
have a more robust way of identifying matches in the face of duplicate
or changing titles
Fix typo introduced by mistake
Centralize logging
Add more complete escaping/conversion of body text

- escape #nnn so it doesn't look like a Github issue reference
- convert Google Code "issue nnn" references to "issue #nnnn" so they
work in Github
Start of issue number mapping between old and new
Merge branch 'master' of git://github.com/arthur-debert/google-code-issues-migrator

Conflicts:
	migrateissues.py
Finish up merge for changes on upstream

- Switch Google Code IDs from string to int to match change made on
upstream
- Modify dummy issue creation to include link to deleted Google Code
issue so mapping works
- remove dependency on enhanced pyGithub
Merge pull request #18 from tfmorris/master

Add cross reference handling, improve error handling