PATCH: extending extend

[Olly Betts]

Thanks for the patch!

Phil Underwood sent me a patch with a very similar intent recently, but
unfortunately I've been rather buried and haven't had time to do much
with it.

I believe your patch offers more sophisticated handling of breaking
loops than Phil's, while his provided the ability to flip the direction
rather of explicitly specifying left and right.  I think both approaches
are useful to have.

Should I forward you Phil's patch and let you two come up with a
combined version?

Cheers,
    Olly