tests/test-cat

Fixing issue1542, adding a relevant test

inotify is smart enough to notify you about any changes in a
directory, even if you only watch the directory, and none if its
contents: the recursive add_watch I added was unnecessary.

The only thing that matters here is the recursive status update on
directory deletion.

And scan() has to be called _before_ the deferred call is registered.
(race condition: depending on the times, the previous patch could
apparently fail on the provided test. It's not the case anymore.)

#!/bin/sh
#
mkdir t
cd t
hg init
echo 0 > a
echo 0 > b
hg ci -A -m m -d "1000000 0"
hg rm a
hg cat a
hg cat --decode a # more tests in test-encode
echo 1 > b
hg ci -m m -d "1000000 0"
echo 2 > b
hg cat -r 0 a
hg cat -r 0 b
hg cat -r 1 a
hg cat -r 1 b