Give seektest .libs dependency so that it gets updated on libavformat changes.

patch by Wolfram Gloger, wmglo dent.med.uni-muenchen de

Originally committed as revision 10246 to svn://svn.ffmpeg.org/ffmpeg/trunk

Makefile

@@ -278,7 +278,7 @@ codectest mpeg4 mpeg ac3 snow snowll: ffmpeg$(EXESUF) tests/vsynth1/00.pgm tests
 libavtest: ffmpeg$(EXESUF) tests/vsynth1/00.pgm tests/asynth1.sw
 	$(SRC_PATH)/tests/regression.sh $@ $(LIBAV_REFFILE) tests/vsynth1
 
-seektest: tests/seek_test$(EXESUF)
+seektest: tests/seek_test$(EXESUF) .libs
 	$(SRC_PATH)/tests/seek_test.sh $(SEEK_REFFILE)
 
 ifeq ($(CONFIG_SWSCALER),yes)