Merge branch 'nd/diff-parseopt'

A brown-paper-bag bugfix to a change already in 'master'.

* nd/diff-parseopt:
parse-options: check empty value in OPT_INTEGER and OPT_ABBREV
diff-parseopt: restore -U (no argument) behavior
diff-parseopt: correct variable types that are used by parseopt

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge

diff --cc parse-options-cb.c
Simple merge

diff --cc parse-options.c
Simple merge

diff --cc t/t4013-diff-various.sh
Simple merge