Set uninitialized inotify_fd to -1, not 0

Currently we set inotify_fd to the value 0 when inotify_fd hasn't been
created yet, or after we close it. But 0 is a valid fd, and we check
for the value -1 to see if it's been initialized. So, if inotify
support is compiled in, but we disable_auto_reload, we can end up
closing fd 0. This can screw up various other things in weird ways,
including that exec'd processes appear to have an invalid stdin.

So, set inotify_fd to -1 to clear all of this up.
Merge pull request #22 from adeason/inotifyfd

Set uninitialized inotify_fd to -1, not 0