We now call pathcopies() from the base to each of the commits, and
that calls _computeforwardmissing(), which does file prefetching (in
the remotefilelog override). So the call to _computenonoverlap() is
now pointless (the sets of files from _computenonoverlap() are subsets
of the sets of files from _computeforwardmissing()).
This somehow also fixes a broken remotefilelog test.