Fix video delay when using alsa or oss as slaves

Decrease poll delay from 0.5 to 0.01 seconds in alsa in oss, else the
audio input would block the video input when used as an input slave.
Other accesses likely to be used as input slaves might need to be
changed. An easier solution (module-wise, harder core wise) would be to
run each slave in its own thread.
(cherry picked from commit 3d9fc421)

modules/access/alsa.c

@@ -318,7 +318,7 @@ static int Demux( demux_t *p_demux )
         }
 
         /* Wait for data */
-        int i_wait = snd_pcm_wait( p_sys->p_alsa_pcm, 500 );
+        int i_wait = snd_pcm_wait( p_sys->p_alsa_pcm, 10 ); /* See poll() comment in oss.c */
         switch( i_wait )
         {
             case 1:

modules/access/oss.c

@@ -273,7 +273,7 @@ static int Demux( demux_t *p_demux )
         }
 
         /* Wait for data */
-        if( poll( &fd, 1, 500 ) ) /* Timeout after 0.5 seconds since I don't know if pf_demux can be blocking. */
+        if( poll( &fd, 1, 10 ) ) /* Timeout after 0.01 seconds. Bigger delays are an issue when used with/as an input-slave since all the inputs run in the same thread. */
         {
             if( fd.revents & (POLLIN|POLLPRI) )
             {