Invoke format_comment even in dry run. Fixes #20.

[jaraco]

I haven't tested this change, but the idea is basically to invoke the comment formatting during the dry run.

[jeffwidman]

Quick FYI for the archives--while the idea here is sound, it's currently throwing an exception for me whenever I try to use the --dry-run option on master at 27c5004

I thought I'd manually tested it properly before merging, but obviously I screwed up...
I was simultaneously working on some other changes to the code and I think I accidentally tested the wrong branch.

I'm just about to go take a look at #36, which I'm guessing will fix this due to the huge refactor, but did want to add a note here just for reference.

The exception I'm hitting:

File "migrate.py", line 363, in <module>
    print u"Comments", [format_comment(options, comment['body'].encode('utf-8', errors='replace')) for comment in comments]
  File "migrate.py", line 131, in format_comment
    comment['user'],
TypeError: string indices must be integers, not str