show_dirstat: simplify same-content check

show_dirstat: simplify same-content check

We use two nested conditionals to store a content_changed
variable, but only bother to look at the result once,
directly after we set it. We can drop the variable entirely
and just use a single "if".

This needless complexity is the result of 2ff3a80334 (Teach
--dirstat not to completely ignore rearranged lines within a
file, 2011-04-11). Before that, we held onto the
content_changed variable much longer.

While we're touching the condition, we can swap out oidcmp()
for !oideq(). Our coccinelle patches didn't previously find
this case because of the intermediate variable, but now it's
a simple boolean in a conditional.

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