gstamchybris.c: in our case, media_codecs.xml is available under /system/etc

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
gstamchybris.c: verifying if compat is available in plugin_init

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
Merge pull request #4 from rsalveti/packaging

Check if the compat layer is available before using it