- Add gcrypt as a checksum module

- Use gcrypt by default

- To use mhash anyway, compile with 'make USE_MHASH=1'

Reviewed-by: Mark Fasheh <mfasheh@suse.de>
- need to free running_checksum object when we are done with it.

Reviewed-by: Mark Fasheh <mfasheh@suse.de>
- Was accidentally passing -lmhash unconditionally in Makefile

Reviewed-by: Mark Fasheh <mfasheh@suse.de>
- Add csum-test.c, a unit-test for the duperemove csum api.

- Script to exercise this will come later, for now the output of
  csum-test can be compared to that of 'sha256sum' to verify that
  the code works as intended.

Reviewed-by: Mark Fasheh <mfasheh@suse.de>
- bump release # so it's easy to identify when we start with libgcrypt.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>