post-receive-email: do not send patches for non-fast-forward changes

We can set -p (or --patch, or -u) to hooks.diffops to send patches in
summary of changes. This is convenient way to see changes. But this
works well for fast-forward pushes only. Some workflows allow rewriting
branches or theirs rebasing upon upstream. In such cases diff patches
carry no useful information about updates. So, disable --patch (and some
similar) option to avoid generating such "broken" patches.

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>