Warn before pulling if a branch appears to have been rebased

[eamodio]

Pulling remote changing into a branch that has been rebased can cause lots of issues, so we should detect this case and warn the user beforehand.

[IAmHopp]

@eamodio Rare that I do this but had to come back here to thank you for this. Has been very helpful!

[eamodio]

@IAmHopp thanks! Glad it helps!