Merge branch 'jc/format-patch-range-diff-fix'

"git format-patch --range-diff" by mistake passed the diff options used to generate the primary output of the command to the range-diff machinery, which caused the range-diff in the cover letter to include fairly useless "--stat" output. This has been corrected by forcing a non-customizable default formatting options on the range-diff machinery when driven by format-patch. * jc/format-patch-range-diff-fix: format-patch: do not let its diff-options affect --range-diff