BugzillaLPPlugin.getCommentIds() and fetchComments() shouldn't expect integer comment IDs from the remote service

At present, the BugzillaLPPlugin.getCommentIds() and fetchComments() methods expect the plugin API's Launchpad.comments() method to return comment IDs as integers. Unfortunately, due to the way that the data being returned from the remote server is interpreted by Python's xmlrpclib (actually the cause of the issue is in the XML-RPC spec), all Bug IDs returned by Launchpad.comments() are strings rather than integers.

fetchComments() and getCommentIds() should be updated to reflect this so as to avoid KeyErrors when looking up the comments for a particular bug.