Merge branch 'jk/format-patch-ignore-noprefix'

Merge branch 'jk/format-patch-ignore-noprefix'

"git format-patch" honors the src/dst prefixes set to nonstandard
values with configuration variables like "diff.noprefix", causing
receiving end of the patch that expects the standard -p1 format to
break.  Teach "format-patch" to ignore end-user configuration and
always use the standard prefixes.

This is a backward compatibility breaking change.

* jk/format-patch-ignore-noprefix:
  rebase: prefer --default-prefix to --{src,dst}-prefix for format-patch
  format-patch: add format.noprefix option
  format-patch: do not respect diff.noprefix
  diff: add --default-prefix option
  t4013: add tests for diff prefix options
  diff: factor out src/dst prefix setup