- Re-instate the fully unconditional "snap-to-last" behaviour in

uniquify().  Mention that "snap-to-last" is a no-op when
    second-to-last point is more than <tolerance> apart from the last
    point.

  - Assert that the <tolerance> is a non-negative value.

  - For benefit of Emacs indenting, adjust license block.

uniquepoints.c

@@ -32,6 +32,7 @@ You should have received a copy of the GNU General Public License
   along with OpenRS.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <assert.h>
 #include <stdlib.h>
 #include <math.h>
 #include <string.h>
@@ -79,11 +80,13 @@ static int createSortedList(double *list, int n, int m,
 
 
 /*-----------------------------------------------------------------
- Remove points that are closer than tolerance in list
- of increasing doubles
+ Remove points less than <tolerance> apart in <list> of increasing
+ doubles.
 */
 static int uniquify(int n, double *list, double tolerance)
 {
+  assert (!(tolerance < 0.0));
+
   if (n<1) return 0;
   int    i;
   int    pos = 0; 
@@ -96,14 +99,19 @@ static int uniquify(int n, double *list, double tolerance)
     }
   }
 
-  /* Keep last value (one way or the other...) */
-#if 0
-  if (val + tolerance < list[n-1]){
+  /*
+    Preserve outer z-boundary.
+
+    This operation is a no-op in the case
+
+          list[pos-2] + tolerance < list[n-1].
+    
+    If, however, the second to last point is less than <tolerance>
+    away from the last point (list[n-1]), we remove this
+    second-to-last point as it cannot be distinguished from "final"
+    point.
+  */
   list[pos-1] = list[n-1];
-  }
-#else
-    list[pos-1] = list[n-1];
-#endif
 
   return pos;
 }