inotify: workaround ENAMETOOLONG by using symlinks
If we can't create the unix socket because the path is too long
we create the socket in a temporary directory and symlink it into
the repo.
Fix issue1208
% fail
failed to contact inotify server: AF_UNIX path too long
deactivating inotify
abort: could not start server: File exists
% inserve
% status
failed to contact inotify server: AF_UNIX path too long
deactivating inotify
? hg.pid