Here are the changes between public POV-Ray 3.1 and 3.1g

 3.1g               04/26/99 Chris Young
 Fixed 4d vector bug

 3.1f               04/22/99 Chris Young
 Fixed problem with missing ) in #write that crashed
 Fixed bump_map bug introduced in 3.1e
 Fixed problem with empty textures
 Fixed #macro inside #while problem
 Traped vnormalize(<0,0,0>)
 Updated copyright, removed compuserve

 3.1e               03/05/99 Chris Young
 Fixed bump_map bug introduced in 3.1a
 Misc unix/linux fixes and cleanups

 3.1d               1/30/99 Chris Young
 Fixed crash in #write of vector or float
 Added #write and #read now support 2d, 4d, & 5d vectors.

 3.1c               1/29/99 Chris Young
 Fixed radiosity preview with odd screen size.
 Reinitialized max_trace_level & radiosity_trace_level properly
 Fixed token at end of file with no cr/lf or newline
 
 3.1b               1/18/99 Chris Young
 Blob elements transformed after textures now works
 Can now declare 2D vectors
 Can now declare 4D vectors
 Can now declare 5D vectors as colors
 Fixed vector.v bug
 Partial fix to bump_map bugs
 Fixed bug involving "once" and "interpolate"
 Fixed reflection leak bug
 Fixed potential GPF in ListReflect
 Fixed normal checker, hexagon bug
 Fixed skysphere with no color_map crash
 Fixed transform identifier parsing problem
 Fixed #local with same name as #declare of different type bug
 Fixed average normal bug and other normal flipping problems
 Removed double_illuminate for normal{} but retained it for 
  smooth_triangle, smoothed height_fields, and bicubic_patch.
  Will redesign in 3.5 and consider added optional keyword double_illuminate.
 Fixed normal{average} with no map crash
 Fixed various conic_sweep prism bugs
 Change in resumed render line numbering
 Fixed focal blur gamma correction bug
 Fixed recursive include overflow bug
 Fixed recursive macro overflow bug
 Fixed #write double closing which crashed Linux
 Delete degenerate smooth_triangles when normals bend too much.
 Many MS-Dos changes so C++ compiler can be used.
 Changed EPSILON small value in MS-Dos version
 
 3.1a               9/29/98 Chris Young
 Fixed problem with sor and lathe affecting unix and amiga
 Fixed fclose in FILE_EXISTS
 Fixed crackle and black_hole use of POV_SRAND.
   Note POV_SRAND and POV_RAND no longer reconfigurable 
   in frame.h or config.h.  If you redefined them on your
   platform -- don't.