[GRASS5] v.support/v.build

[Radim Blazek]

Hi,

I spent a long time by looking for why clean data are not build properly.
I hope, I found the problem:
1. m.in.e00 sets:  map.head.orig_scale = 100000l;
2. v.build sets: Map.snap_thresh = THRESH_FUDGE * Map.head.orig_scale *       
                      dig_unit_conversion();
3. dig_calc_begin_angle() calculates wrong angle if thresh is too big, because
    it takes first point outside threshold
4. dig_build_area_with_line() fails to build area because line order is not   
    correct

As a solution, I have changed v.build, so that it sets snap_thresh only if it 
is specified on command line. (Threshold is now printed by v.info).
Default snap_thresh is set by Vect__init_head() to 0.0, so threshold should
be zero until user changes threshold value by v.support parameter.

In addition i have added new option "err=" to v.support/v.build, which is
name of new error vector, where are saved area edges with topology
problems, so that it is possible display only that lines over original map. 
For bad edges is also error message printed by v.support now.

If anybody had problems with "clean" polygon data imported by v.in.e00, please
test now (v.support map=xxx threshold=0 err=err).

Radim