Replace many includes of libavutil/common.h with what is actually needed

This reduces the number of false dependencies on header files and
speeds up compilation.

Originally committed as revision 22407 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/sha.c

@@ -21,8 +21,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#include "common.h"
-#include "avutil.h"
+#include <string.h>
 #include "bswap.h"
 #include "sha.h"
 #include "sha1.h"