Change SDL resource loading to use our filesystem functions

SDL 1.2's own filesystem functions have very limited unicode support,
so provide an SDL_RWops struct to let them use ours.
This also bumps the minimum required SDL_mixer version to 1.2.12

Conflicts:
	SConstruct
	src/filesystem.hpp
Add a Raring repository to travis

This is to allow a newer version of SDL_mixer to be installed.

Conflicts:
	.travis.yml
replace raring with saucy, raring is gone...
Merge pull request #303 from cbeck88/troubleshooting_travis

SDL RW Ops (master, new)