* two functions to handle allocation of static data more simple

* two functions to handle allocation of static data more simple
  av_mallocz_static - called for every static data table
  av_free_static - called when ffmpeg is no longer needed and should free
                   all static resources
* simple usage shown in mpegaudiodec.c

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@1301 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b