Rename the CMakeModules directory to simply cmake.

This is more consistent with the other directories in the project.
Fix incorrect cast to ssize_t.

gcc 4.2.1 warns about a possible incorrect cast to ssize_t when comparing against refcount, which is of type size_t. signed vs unsigned comparison.

Sinc warnings are treated as errors (as in the autoconf project) this would cause a compile error.
Compile tests by default.

- Encourage actually using the unit tests by compiling them by default.
Set the WITHOUT_TESTS variable to build without instead...

- Changed comments to keep within 80 characters.
- Don't have a hard coded path for valgrind, simply assuem it's in the path instead (an OSX ports install puts it in /opt/local/bin for instance).
- Fixed building the shared lib.