pull:create fails when using an older git version

Since the resent change with getting the default title for the PR it fails on my system.
It seems `fork-point` was introduced in git 1.9 / 2.0 and does not exist in the version I'm using `1.8.4.msysgit.0`.

I can upgrade this version, but I'm not sure which Git version is provided with most Unix-type systems.
So should warn the user if the Git-version is to low or disable this behavior for such cases?