tests/test-mactext.t

perf: add threading capability to perfbdiff

Since we are releasing the GIL during diffing, it is interesting to see how a
thread pool would perform on diffing. We add a new `--threads` argument to
commands. Synchronizing the thread pool is a bit complex because we want to be
able to reuse it from one run to another.

On my computer (i7 with 4 cores + hyperthreading), I get the following data for
about 12000 revisions:
threads wall        comb    wall gain   comb overhead
none    31.596715   31.59    0.00%       0.00%
1       31.621228   31.62   -0.08%       0.09%
2       16.406202   32.8    48.08%       3.83%
3       11.598334   34.76   63.29%      10.03%
4        9.205421   36.77   70.87%      16.40%
5        8.517604   42.51   73.04%      34.57%
6        7.94645    47.58   74.85%      50.62%
7        7.434972   51.92   76.47%      64.36%
8        7.070638   55.34   77.62%      75.18%

Compared to the feature disabled (threads=0), the overhead is negligible with
the threading code (threads=1), and the gain is already 48% with two threads.

  $ cat > unix2mac.py <<EOF
  > import sys
  > 
  > for path in sys.argv[1:]:
  >     data = file(path, 'rb').read()
  >     data = data.replace('\n', '\r')
  >     file(path, 'wb').write(data)
  > EOF
  $ cat > print.py <<EOF
  > import sys
  > print(sys.stdin.read().replace('\n', '<LF>').replace('\r', '<CR>').replace('\0', '<NUL>'))
  > EOF
  $ hg init
  $ echo '[hooks]' >> .hg/hgrc
  $ echo 'pretxncommit.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
  $ echo 'pretxnchangegroup.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
  $ cat .hg/hgrc
  [hooks]
  pretxncommit.cr = python:hgext.win32text.forbidcr
  pretxnchangegroup.cr = python:hgext.win32text.forbidcr

  $ echo hello > f
  $ hg add f
  $ hg ci -m 1

  $ $PYTHON unix2mac.py f
  $ hg ci -m 2
  attempt to commit or push text file(s) using CR line endings
  in dea860dc51ec: f
  transaction abort!
  rollback completed
  abort: pretxncommit.cr hook failed
  [255]
  $ hg cat f | $PYTHON print.py
  hello<LF>
  $ cat f | $PYTHON print.py
  hello<CR>