Fix unrecognized option errors when building with older versions of GCC (Issue #23).

This approach suggested by ppannuto.
Clean up GCC flags

Remove some redundant or repeated flags, as noted by ppannuto in Issue #23.
Clean up Makefile success output
Remove Redis objects on make clean

Resolves Issue #33.
Undefine _FORTIFY_SOURCE before defining it, in case it's set by the distro.

Fixes Issue #7.