Fedora/Non-Symlink Support

[isantop]

This adds support for systems which don't use the /vmlinuz and /initrd.img symlinks for kernel management. This includes changes which allow it to operate automatically following a kernel upgrade and logic changes for version detection. It also makes the dependency on python-debian a soft dependency, and attempts to fallback on python-rpm if it isn't available. These changes should not affect the usage of kernelstub on debian-based OSs.