Declare struct SwsContext before using it, fixes the checkheaders warning:

libswscale/swscale_internal.h:58: warning: `struct SwsContext' declared inside parameter list
libswscale/swscale_internal.h:58: warning: its scope is only this definition or declaration, which is probably not what you want


git-svn-id: file:///var/local/repositories/mplayer/trunk/libswscale@28353 b3059339-0415-0410-9bf9-f77b7e298cf2

swscale_internal.h

@@ -52,6 +52,8 @@
 #   define APCK_SIZE 16
 #endif
 
+struct SwsContext;
+
 typedef int (*SwsFunc)(struct SwsContext *context, uint8_t* src[], int srcStride[], int srcSliceY,
              int srcSliceH, uint8_t* dst[], int dstStride[]);