The GitHub UI treats `#NUMBER` as referring to its own issues which is confusing
when in jQuery source it's usually referring to the old deprecated Trac instance
at https://bugs.jquery.com. This change replaces all such Trac references with
`trac-NUMBER`.
A few of the references came with the Sizzle integration and referred to the
Sizzle GitHub bug tracker. Those have been replaced with full links instead.
A new entry describing issue reference conventions has been added to README.
Closes gh-4993
Also, run `grunt npmcopy` to sync the "external" directory with dependencies
from package.json. For example, the Sinon library version didn't match.
Ref gh-4234
Closes gh-4297
This commits backports some changes done in the patch to the then-existing
compat branch that removed support for old browsers and added some support
comments.
Refs 90d7cc1d8b