git-commit: use printf '%s\n' instead of echo on user-supplied strings
git-commit: use printf '%s\n' instead of echo on user-supplied strings

This fixes the same issue git-am had, which was fixed by Jeff
King in the previous commit.  Cleverly enough, this commit's log
message is a good test case at the same time.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

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