Fix for github-1.0 PortGroup to test

[Michael Dickens]

The github PortGroup is not selecting the livecheck type correctly
because the regexp isn't correct (or, that's the way I debug it).
Also, strings should be compared using "eq" and so forth ([string
equals ...] should work, but "eq" is easier to read IMHO).  So, here's
a patch I'm proposing to fix these, and add a comment as to what the
regexp is trying to accomplish.  This fix works for both commits and
tags for me (I did not try a combined commit/tag), but I'd like some
others to verify before I commit it.  Thanks! - MLD
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