Add delaunay and constrained triangulation

Two new functions have been added

```sql
ST_Delaunay(GEOMETRY) or ST_Delaunay(GEOMETRY, INT) 
```
Creates a delaunay triangulation and returns a collection of geometry.

```sql
ST_ConstrainedDelaunay(GEOMETRY) or ST_ConstrainedDelaunay(GEOMETRY, INT)
```
Creates a constrained delaunay triangulation and returns a collection of geometry.

Note if the Z value is equal to NaN the algorithm set a 0 value ordinate.


Comparing to Postgis the first function is a bit different

```sql
ST_DelaunayTriangles(geometry g1, float tolerance, int4 flags);
```
URL = http://postgis.org/documentation/manual-2.1SVN/ST_DelaunayTriangles.html

We decide to delete the word Triangles because we think that is a nonsense. The output is set with the int flat 0 for multipolygon (triangles) and 1 for multilinestring (edges) so if a user set ST_DelaunayTriangles(GEOMETRY, 1) it returns edges and not Triangles.  Moreover a delaunay triangulation is used to create a mesh of triangles ;-)