Added a possibility to flatten the interface meshes when creating projectors. This enables simple joining of fields with different dimensions, mainly 3D->2D. Also added possibility to optionally use (s,z) coordinate system for rotational projectors instead of (phi,z). The 1st has the advantage that the arc length, s, is in the same units as the z coordinate. 


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6763 04224531-1f84-46d8-96ce-875b9e37dce3
Test case for mixed dimensional models joined by a mortar (periodic) interface. 


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6764 04224531-1f84-46d8-96ce-875b9e37dce3