Restored the free_imbuf_seq_except() in sequencer, to free all memory

of sequencer, except current frame. Apparently the cache limitor doesnt
work for floatbuffers yet... and while rendering, I prefer to have all
memory available for the render itself.

Schlaile; you might check on what is wrong, in case imbufs have have
a rect_float or zbuf_float, the cache doesnt work yet?

source/blender/src/sequence.c

@@ -2741,9 +2741,10 @@ void do_render_seq(RenderResult *rr, int cfra)
 		/* 	R.rectz = BLI_dupallocN(ibuf->zbuf); */
 		/* } */
 
-		/* Let the cache limitor take care of this
-		   free_imbuf_seq_except(cfra);
-		*/
+		/* Let the cache limitor take care of this (schlaile) */
+		/* no, doesnt seem to work for float buffer? (ton) */
+		free_imbuf_seq_except(cfra);
+		
 	}
 	G.f &= ~G_PLAYANIM;