(bug 46444) allow opening parentheses before git/gerrit references

I was considering allowing a few different characters; primarily a
slash '/' and a plus '+', but I decided that they're too likely to
appear in URLs and thus again cause the issue that was the reason this
regex was crafted in the first place (bug 40344).

Change-Id: Iaf6963424dab3918628c6b0c73c331405dd8fa21