The Checksum class interface was changed in a way that caused the tests to fail.
The Checksum class defines an interface which the SHA1Checksum and CRC32Checksum implement. Added test unit test cases to verify that the checksums work and perform as expected.
Now, given a concept xyz, * the main test file is called test_xyz.cc * the executable is called test_xyz, and * the ctest test is called text_xyz.
