Fix OLD_T_NEW after v.in.dxf

Patches from geni.knu.ac.kr:

Fixed OLD_T_NEW errors with d.vect and related programs after v.in.dxf.
This is not d.vect bug. v.in.dxf puts header info at the wrong location.

ftp://geni.knu.ac.kr/pub/geni/patch/grass/grass5.0beta8-CVS/patch.rt3.gz

README.rt3
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1. v.in.ascii misread DIGIT DATE info.

  DIGIT DATE: Thu Jun 1 23:19:39 2000
   G_rindex(buff,':') locate ptr here ^, this means DIGIT DATE is "39 2000".

   Instead, G_index(buff,':') locate ptr
  DIGIT DATE: Thu Jun 1 23:19:39 2000
                  ^
   now DIGIT DATE has correct value "Thu Jun 1 23:19:39 2000".

   This helps with other info including ':'.

2. d.vect and related programs cause OLD_T_NEW errors. This is because
   v.in.dxf and v.in.dxf2 creates broken vector files with wrong header.

   In case fp is opened using G_fopen_append, fseek(fp,0L,0) points EOF.
   So, if file is already opened for adding geo info, fp should be closed
   and reopened using G_fopen_modify.

   Is this only problem of FreeBSD?

Regards,
Huidae Cho