Merge branch 'rs/diff-no-index-cleanup'

"git diff --no-index A B" managed its the pathnames of its two
input files rather haphazardly, sometimes leaking them.  The
command line argument processing has been straightened out to clean
it up.

* rs/diff-no-index-cleanup:
  diff-no-index: simplify argv index calculation
  diff-no-index: release prefixed filenames
  diff-no-index: release strbuf on queue error