scmutil: teach the file prefetch hook to handle multiple commits
The remainder of the commands that need prefetch deal with multiple revisions.
I initially coded this as a separate hook, but then it needed a list of files
to handle `diff` and `grep`, so it didn't seem worth keeping them separate.
Not every matcher will emit bad file messages (some are built from a list of
files that are known to exist). But it seems better to filter this in one place
than to push this on either each caller or each hook implementation.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.