(svn r4901) - Codechange: change 'SpriteGroup *' to 'struct SpriteGroup *' within StationSpec and GRFFile struct declarations. Now only code which actually references those pointers needs to know about the SpriteGroup struct. Remove some unnecessary lingering header dependencies.

/* $Id */

KNOWN BUGS / PROBLEMS:

Normal and elrail depots look the same. Use 'X' (transparent buildings)
   to distinguish between them
Missing curors / icons for construction (currently using the conventional ones)