2nd try at committing to trunk (instead of particles branch) :)

Fixes for bugs in #7833
- Hair softbody cache was reset on rendering.
- When Alt-a playback is synced to audio frames are skipped. This caused dynamics caching to go crazy. Now the first loop of playback goes through all frames if there are non cached dynamic systems.

Invalid point caches weren't cleared when new systems were created. This caused messed up shapes when softbody was added.

source/blender/src/buttons_object.c

@@ -3248,6 +3248,7 @@ static void object_softbodies__enable(void *ob_v, void *arg2)
 		if (!ob->soft) {
 			ob->soft= sbNew();
 			ob->softflag |= OB_SB_GOAL|OB_SB_EDGES;
+			softbody_clear_cache(ob, CFRA);
 		}
 	}
 	/* needed so that initial state is cached correctly */
@@ -3281,6 +3282,7 @@ static void object_softbodies__enable_psys(void *ob_v, void *psys_v)
 			psys->soft= sbNew();
 			psys->softflag |= OB_SB_GOAL|OB_SB_EDGES;
 			psys->soft->particles=psys;
+			clear_particles_from_cache(ob, psys, CFRA);
 		}
 		psys->softflag |= OB_SB_ENABLE;
 	}