[GRASS5] clean, build

[Radim Blazek]

I have done some optimization in cleaning functions and build
process. Build and cleaning should be now faster and more reliable.
However, maybe that I introduced new bugs, especially in point
in polygon/area function and assigning of isles and centroids to areas
could fail. 
v.in.ogr without '-c' option should now in theory create clean file
which builds without "Number of incorrect boundaries" (i.e. 0).
I am interested in data where it fails, v.build error= can 
extract errors from the vector.

Radim