Matt Harbison <matt_harbison@yahoo.com> [Sun, 11 Feb 2018 00:23:57 -0500] rev 36175
cmdutil: convert the prefetchfiles() hook to a callback mechanism (API)
Yuya suggested a list of callbacks instead of function wrapping. This means
that one extension can't block another from processing the list.
.. api::
File prefetching is now handled by registering a callback with
scmutil.fileprefetchhooks.