diff-no-index: replace manual "."/".." check with is_dot_or_dotdot()
diff-no-index: replace manual "."/".." check with is_dot_or_dotdot()

Helped-by: Eric Sunshine <8d6e34f987851aa599257d3831a1af040886842f@sunshineco.com>
Signed-off-by: Brian Bourn <9fa6bb2da9530d72e8a505a9b61e37dcdb363f68@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git