PPM image support

PPM image format is already supported in FFMPEG. It would be possible to
support it in vlc too with the following patch.
The targetted usage of this change is to be able to do:
vlc --fake-file image.ppm fake://
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

src/misc/image.c

@@ -541,6 +541,7 @@ static const struct
     { VLC_CODEC_TIFF,              "tif" },
     { VLC_CODEC_TIFF,              "tiff" },
     { VLC_FOURCC('l','b','m',' '), "lbm" },
+    { VLC_FOURCC('p','p','m',' '), "ppm" },
     { 0, NULL }
 };