match: remove unnecessary '^' from regexes
The regexes are passed to re.match(), which matches against the
beginning of the input, so the '^' doesn't do anything.
Note that unrooted patterns, such as globs and regexes from .hgignore
are instead achieved by adding '.*' to the expression given by the
user. (That's unless the user's expression started with '^', in which
case the '.*' is not added, perhaps to keep the regex cleaner?)