diff.c: add "const" qualifier to "char *cmd" member of "struct ll_diff_driver"
diff.c: add "const" qualifier to "char *cmd" member of "struct ll_diff_driver"

Also use "git_config_string" to simplify code where "cmd" is set.

Signed-off-by: Christian Couder <ddbaab5867ed34fd53535b58c9cdd59abd2e2aff@tuxfamily.org>
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