Replaced is_multi by tag_cast as planned (see also http://barendgehrels.blogspot.com/2010/10/tag-dispatching-and-inheritance.html)

Moved num_geometries to algorithms/ folder
Created new file num_interior_rings.hpp (extracted from interior_rings.hpp)


[SVN r68803]

libs/geometry

@@ -1 +1 @@
-Subproject commit 6a886721e76f3daa940409b9bef829e15e429076
+Subproject commit 4faf0f235d8b33cba18369bf38e32033b9377701