t1512: ignore whitespaces in wc -l output

Some implementations of sed (e.g. MacOS X) have whitespaces in the
output of "wc -l" that reads from the standard input.  Ignore these
whitespaces by not quoting the command substitution to be compared
with the constant "16".

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

t/t1512-rev-parse-disambiguation.sh

@@ -257,7 +257,7 @@ test_expect_success 'rev-parse --disambiguate' '
 	# commits created by commit-tree in earlier tests do not share
 	# the prefix.
 	git rev-parse --disambiguate=000000000 >actual &&
-	test "$(wc -l <actual)" = 16 &&
+	test $(wc -l <actual) = 16 &&
 	test "$(sed -e "s/^\(.........\).*/\1/" actual | sort -u)" = 000000000
 '