Add testvalgrind make target for checking for memory leaks

Aman,

As discussed I think that switching from minunit to cmocka as a unit test framework may slow you down.

I understand that cmocka does some memory checks. This pull request invokes valgrind (memcheck) in all the tests, and the output needs to be eye-balled for lost memory. I think it may be helpful as a simple quick solution for memory checks.