supertux/supertux-qvga : migrate to inc file, and fix supertux-qvga configure

supertux/supertux-qvga : migrate to inc file, and fix supertux-qvga configure

supertux_0.1.3 and supertux-qvga_0.1.3 were doing that:
  supertux_0.1.3: PR = "r6"
  supertux-qvga_0.1.3: require supertux_${PV}.bb
And supertux-qvga didn't redefine PR

So I had to convert move supertux_0.1.3 to supertux.inc
  and convert everything to inc_PR

supertux-qvga needed 2 things to configure tough:
*depending on libsdl-gfx(supertux can build without):
    checking for rotozoomSurface in -lSDL_gfx... no
    configure: error: SDL_gfx library required
* fix the following error:
    checking for Mix_OpenAudio in -lSDL_mixer... no
    configure: error: SDL_mixer library required
  The fix is similar to ac36d86725da867d691b16668d88f096d0b7da37
    ( libsdl-mixer 1.2.11: fix libvorbis's search path )
  And the cause is the same:
    configure:5791: arm-oe-linux-gnueabi-gcc [...] conftest.c -lSDL_mixer -lSDL -lpthread -L/usr/lib -lmikmod -ldl -lm >&5
    /usr/lib/libSDL_mixer.so: file not recognized: File format not recognized
    collect2: ld returned 1 exit status

Note that the packages were visually inspected with find in :
    supertux-0.1.3-r7.0/packages-split
    supertux-qvga-0.1.3-r7.0/packages-split

PR was bumped in supertux.inc

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>