hook: only redirect stdout if it and stderr are valid files
When using hgwebdir with WSGI via the IIS ISAPI-WSGI extension, both
stdout and stderr filenos are set to -2, which makes the os.dup call
in hook.py fail.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.