Add vorbis_version_string to the dll export list.
Add vorbis_version_string to the dll export list.

Patch by Aoyumi. This is a followup to the addition of this api call
in r15346.

svn path=/trunk/vorbis/; revision=15530

felipebetancur/vorbis,mwgoldsmith/vorbis,nicolaichuk/vorbis,mwgoldsmith/vorbis,ShiftMediaProject/vorbis,ShiftMediaProject/vorbis,mwgoldsmith/vorbis,nicolaichuk/vorbis,emscripten-ports/Vorbis,eidy/vorbis,ShiftMediaProject/vorbis,ksophocleous/vorbis,eidy/vorbis,felipebetancur/vorbis,erikd/vorbis,ksophocleous/vorbis,ShiftMediaProject/vorbis,emscripten-ports/Vorbis,nicolaichuk/vorbis,ShiftMediaProject/vorbis,erikd/vorbis,youfearm3/vorbis,felipebetancur/vorbis,emscripten-ports/Vorbis,felipebetancur/vorbis,ShiftMediaProject/vorbis,youfearm3/vorbis,mwgoldsmith/vorbis,nicolaichuk/vorbis,erikd/vorbis,erikd/vorbis,youfearm3/vorbis,emscripten-ports/Vorbis,ksophocleous/vorbis,eidy/vorbis,eidy/vorbis,youfearm3/vorbis,ksophocleous/vorbis