diff: accept --no-follow option

diff: accept --no-follow option

Once you do

	$ alias glogone git log --follow

there is no way to say

	$ glogone --no-follow ...

Not that "log --follow" is all that useful, but it is cheap to
support the common "you can defeat an undesirable option with a
'no-' variant of it later on the command line" pattern.

Signed-off-by: Junio C Hamano <gitster@pobox.com>