doc: consistently use ASCIIDOC_EXTRA
doc: consistently use ASCIIDOC_EXTRA

For all uses of $(ASCIIDOC) in Documentation/Makefile, supply the same
options via $(ASCIIDOC_EXTRA).

Signed-off-by: Eric Blake <d9321fbaaa1b2c44636b6b3e2377f13b1584bbd6@byu.net>
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