Require at least 8 edges to define a full circle (#2420)

git-svn-id: http://svn.osgeo.org/postgis/branches/2.0@11780 b70326c6-7e19-0410-871a-916f4a2858ee
Require all arc edges to form the same angle (#2423)

Note: gives expected result for #183

git-svn-id: http://svn.osgeo.org/postgis/branches/2.0@11781 b70326c6-7e19-0410-871a-916f4a2858ee
Add NEWS items about #2420 and #2423

git-svn-id: http://svn.osgeo.org/postgis/branches/2.0@11782 b70326c6-7e19-0410-871a-916f4a2858ee