(bug 41903) Adding GitHub support to Bugzilla see also field.

This commit imports the following patch:
http://bzr.mozilla.org/bugzilla/trunk/revision/8202

Upstream bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=704999

This patch has been applied to clean 4.2.4 Bugzilla files.

Thank you to Andre to have found it.

Change-Id: I061a66339e153bc3990f52c3991ee58130254389
Merge "(bug 41903) Adding GitHub support to Bugzilla see also field."