intercept: Allow Steam to use private libx264

Turns out Steam has a vendored x264 library to allow streaming, but right
now we're not whitelisting it. Fix that for issue #25.

Signed-off-by: Ikey Doherty <ikey@solus-project.com>

src/intercept/main.c

@@ -52,6 +52,7 @@ static const char *steam_allowed[] = {
         "libavresample.so.",
         "libavutil.so.",
         "libswscale.so.",
+        "libx264.so.",
 
         /* core plugins */
         "chromehtml.so",