Fixes for unity_fixture

The unity_fixture code in extras/fixture had a few issues that this branch fixes.

1. The tests didn't pass on Unix systems with the latest tools
2. Compilation warnings related to hooking into malloc, described here: http://forums.pragprog.com/forums/123/topics/10901
3. IGNORE_TEST() runs didn't always reliably count ignored tests, described here: http://forums.pragprog.com/forums/123/topics/10126
4. IGNORE_TEST() didn't react to the -v flag. Also described in the previous link.

There are still some outstanding issues with the unity_fixture. Its tests don't get run by the main rakefile, which is probably why they stopped passing, and its test suite isn't comprehensive. These fixes should at least improve the situation, though.