hgk: add .diff extension when exporting commits
Append the .diff extension automatically.
all()draft()::tipdraft() and ::tip0::tiproots(0::tip)author(lmoscovicz)author(mpm)author(lmoscovicz) or author(mpm)tip:0max(tip:0)min(0:tip)0::min(0::)roots((tip~100::) - (tip~100::tip))::p1(p1(tip))::