Changes to est_ep_vec in sparse_disp.in to use only the central 68% of the disparities in estimating the epipolar vector.  Fixed an earlier bug that Oleg found, by replacing > and < with >= and <=, respectively.
add recalc_disp chack to sparse_disp

When the refinement loop finished early, all_pts and nbhd_range were inconsistent.  If this happens, recalculate both.
sparse_disp: Use python >= 2.6
DemDisparity: Allow dem_accuracy == 0
Rename DEM acuracy to DEM error. Add documentation
Minor doc work
point2dem: Make default K=1

Projections error out if K is zero. Most people want 1.