youtube_title.tcl: handle HTTPS and youtu.be URLs

YouTube started defaulting to HTTPS some time ago so share
URLs which made the youtube_title.tcl no longer match pasted
links.  Simply changing the paattern to match HTTPS would not
work though because the script is not able to fetch data over
HTTPS.  Instead, all URLS pasted on the channel are first
changed to HTTP.  See [1].

While at it, the pattern has been changed to support youtu.be
URLs as well as the full youtube.com URLs.

At the same time though, the pattern is now more strict which,
however, should not negativelly affect anything, but instead
prevent the script from matching arbitrary links such as
evilyoutube.com.

[1] http://forum.egghelp.org/viewtopic.php?p=100144#100144