hook: be prepared for __stdout/err__ not having fileno()
it may have been replaced, see https://bitbucket.org/tortoisehg/thg/issue/937
test that 'hg commit' does not crash if the user removes a newly added file
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ touch b
$ hg add b
$ rm b
$ hg commit -A -m"comment #1"
removing b
nothing changed
[1]