Fix compilation error due to missing include.

This fixes compilation error due to missing header.

 SDL_anigif.cpp: In function ‘int AG_LoadGIF_RW(SDL_RWops*, AG_Frame*, int)’:
 SDL_anigif.cpp:293:37: error: ‘malloc’ was not declared in this scope
   gd = (gifdata*)malloc( sizeof(*gd) );
                                     ^
 SDL_anigif.cpp:418:11: error: ‘free’ was not declared in this scope
   free( gd );
           ^
 make: *** [TexturePacker] Error 1
Fix compilation error related to removed structure field by ffmpeg.

ffmpeg removed reference_dts field in struct AVStream.

Related ffmpeg commit:
  http://git.videolan.org/?p=ffmpeg.git;a=commitdiff;h=2ba68dd044ca8fc591139c05563840f546a9c0c0
Merge pull request #3871 from gfto/fix-compile-errors2

Fix two compilation errors.