tests/test-issue436

setup.py: skip inotify if there's no inotify_add_watch

Debian Etch doesn't include a sys/inotify.h header, which makes it
impossible to compile _inotify.c, making hg uninstallable.

The cc.has_function() method is implemented by trying to compile a
simple C program.  Since there's no redirection involved all error
messages are sent to the terminal.  This is not particularly pretty
but at least it allows the installation to complete.

#!/bin/sh

hg init a
cd a
hg -v log -v
hg -v log -v x
true