Fix parsing of label changes from comments.

Label changes weren't being picked up anymore, due to their content
being spread across multiple lines. This wasn't being handled by the
original code at all. We now consolidate these lines, parse them for the
labels, and filter out blank entries.
Strip the content of field changes in the parser.

The field changes parsed out from the page contained extra whitespace.
This applied to the owner, summary, and status. We now strip the
whitespace from these when parsing, and for good measure, we strip the
whitespace for labels as well.