Fix bloomd to build with GCC 4.7.2 warnings mostly on

- This is what caught issue #7 (an argument for accepting the patch :-))
- Couldn't figure out how to get SCons to use Clang, so that is untested
- In test_hashmap.c, I wasn't sure what 'void *foo = 0 & i' was supposed
  to accomplish -- 0 & i will be 0 for any i, and an integer type (not
  pointer). I changed it to 'void *foo = (void*)(intptr_t)i'.
- Everything else is pretty straightforward. Plenty of easily fixed
  'comparison between signed and unsigned' and some 'unused variables'
  in the test code.

CR: gcc, tests pass