test-tool regex: call regfree(), fix memory leaks

test-tool regex: call regfree(), fix memory leaks

Fix memory leaks in "test-tool regex" which have been there since
c91841594c2 (test-regex: Add a test to check for a bug in the regex
routines, 2012-09-01), as a result we can mark a test as passing with
SANITIZE=leak using "TEST_PASSES_SANITIZE_LEAK=true".

We could regfree() on the die() paths here, which would make some
invocations of valgrind(1) happy, but let's just target SANITIZE=leak
for now. Variables that are still reachable when we die() are not
reported as leaks.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>