Remove references to Bugzilla

Replace any such references with references to GitHub, as appropriate.
Leave "dw-bugzilla@" email addresses alone.
Remove last bugs.dwscoalition.org references

Fixes #663. Both the references here removed were links to further docs
of what had been done, rather than notices about outstanding bugs, in
any case.
Actually fixes #663

Add a temporary explanatory note about the broken link to the CLA, and
what to do about it.
Change names of updates strings

Avoid later trouble in this way.  Simply append "2" in two places, in
each of two files, to fix commit before last.
Merge pull request #698 from Darael/bug663-bz-to-ghi

Fix #663 - Bugzilla to GitHub Issues migration