Fixed error() value after failed initialize()

Need to store errno, not the return value from inotify_init()
(which will simply be -1 on error).
Improve error message on initialization failure

Include the error code.

Include a hint about increasing /proc/sys/fs/inotify/max_user_instances
where appropriate.

Don't request emailed bug reports for this; initialization failure isn't
likely to be a bug in inotify-tools.