sws_flags is unsigned.

This together with the last commit fixes the strange behavior of -sws_flags.
(issue229)

Originally committed as revision 12325 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -206,7 +206,7 @@ static uint64_t limit_filesize = 0; //
 static int pgmyuv_compatibility_hack=0;
 static float dts_delta_threshold = 10;
 
-static int sws_flags = SWS_BICUBIC;
+static unsigned int sws_flags = SWS_BICUBIC;
 
 static const char **opt_names;
 static int opt_name_count;