Add a poor implementation of absolute_path for ruby 1.8.

It turns out that the 'real' one was only added in 1.9.1, so this
works around that.
Better fix for the UTF8 issue.

Ruby 1.8 doesn't like unicode BOMs.
Use RUBY_VERSION as this is actually present in 1.9.

No idea why VERSION got removed.. but this works in both 1.8 & 1.9.
Use a fixed path to require the fetch helper.

I'm not sure what the 'correct' fix for this is, but this at least
seems to work both under rbot and manually, allowing for both dev
and deploy scenarios.
Be more restrictive about ticket matching when listening.

We don't want to match numbers that happen to be in url anchors for
isntance. However, do allow just numbers in direct messages as here
it's clearer what's happening & highly unlikely we'll have pages
that are made only from numbers.

Change-Id: I56ead4cf1ea9db1bc7de8589f42a75b8a5ba9101