"git-apply --check" should not report "fixed"

"git-apply --check" should not report "fixed"

When running "git apply --check" while --whitespace=fix is
enabled (either from the command line or via the configuration),
we reported that "N line(s) applied after _fixing_", but --check
by itself does not apply and this message was alarming.

We could even reword the message to say "N line(s) would have
been applied after fixing...", but this patch does not go that
far.  Instead, we just make it use the "N lines add whitespace
errors" warning, which happens to be a good diagnostic message a
user would expect from the --check option.

Signed-off-by: Junio C Hamano <gitster@pobox.com>