rev-list: handle %x00 NUL in user format

The code paths for showing commits in "git log" and "git
rev-list --graph" correctly handle embedded NULs by looking
only at the resulting strbuf's length, and never treating it
as a C string. The code path for regular rev-list, however,
used printf("%s"), which resulted in truncated output. This
patch uses fwrite instead, like the --graph code path.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4012-diff-binary.sh

@@ -77,10 +77,6 @@ test_expect_success 'apply binary patch' \
 	 tree1=`git write-tree` &&
 	 test "$tree1" = "$tree0"'
 
-nul_to_q() {
-	perl -pe 'y/\000/Q/'
-}
-
 test_expect_success 'diff --no-index with binary creation' '
 	echo Q | q_to_nul >binary &&
 	(: hide error code from diff, which just indicates differences