Remove debug at PullRequest initialization

Cause unnnecessary calls to get_issue()
Derive MockTest from MoxTestBase class
Add TestPullRequest suite to test PullRequest using mox
Manage comment counting in create_issue() and create_comment()
Add unit tests to cover parse_body() and parse_comments()
Add tests for parse() method
Add support  for unicode PR titles and users

Define __unicode__() method and __str__() method that encodes its output.
Closes #111
Merge pull request #112 from sbesson/111_pr_mocktesting

Add unit testing for the PullRequest object