With a272b9e70a (urlmatch: allow globbing for the URL host part,
2017-01-31), Git has started to allow globs for the URL host part when
matching config keys like `http.http://*.example.com.proxy` to a
specific URL. But the regular expression we use to verify the config key
does not allow for globs to appear, and thus we refuse such keys even
though they are in fact valid and useful.

Fix this bug by allowing globs.

Changelog: fixed