Allow index scans in edge splitting and healing queries (#3000)

Speeds up topology population when input edges intersect.

A simple test splitting and re-healing an edge in a ~500k edges
topology completes in ~1/10 of the time.

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@13167 b70326c6-7e19-0410-871a-916f4a2858ee