tests/test-revlog-mmapindex.t

tests: demonstrate a problem with renames on the p2 side of a conversion

I think this is related to the octopus merge being sloppy, and that's having a
cascading affect on the fixup merge.  If this change is made on p1 (specifically
with the 'Added parent file' commit), the failure doesn't occur.

The file modification with the rename doesn't seem to be necessary, but it's
what's happening in a production repo where I first noticed, so I left it.  This
is an example of the manifest divergence I'd been seeing, which wasn't fixed by
Yuya's recent changes.  This is separate from the changelog divergence I was
also seeing[1].  Probably nobody cares about bzr anymore, but this will also
affect git, since the octopus fixup code is in the hg sink.

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-August/120473.html

create verbosemmap.py
  $ cat << EOF > verbosemmap.py
  > # extension to make util.mmapread verbose
  > 
  > from __future__ import absolute_import
  > 
  > from mercurial import (
  >     extensions,
  >     pycompat,
  >     util,
  > )
  > 
  > def extsetup(ui):
  >     def mmapread(orig, fp):
  >         ui.write(b"mmapping %s\n" % pycompat.bytestr(fp.name))
  >         ui.flush()
  >         return orig(fp)
  > 
  >     extensions.wrapfunction(util, 'mmapread', mmapread)
  > EOF

setting up base repo
  $ hg init a
  $ cd a
  $ touch a
  $ hg add a
  $ hg commit -qm base
  $ for i in `$TESTDIR/seq.py 1 100` ; do
  > echo $i > a
  > hg commit -qm $i
  > done

set up verbosemmap extension
  $ cat << EOF >> $HGRCPATH
  > [extensions]
  > verbosemmap=$TESTTMP/verbosemmap.py
  > EOF

mmap index which is now more than 4k long
  $ hg log -l 5 -T '{rev}\n' --config experimental.mmapindexthreshold=4k
  mmapping $TESTTMP/a/.hg/store/00changelog.i
  100
  99
  98
  97
  96

do not mmap index which is still less than 32k
  $ hg log -l 5 -T '{rev}\n' --config experimental.mmapindexthreshold=32k
  100
  99
  98
  97
  96

  $ cd ..