[NEW] Enable setting of BCs (and body forces) such that constant value is enforced on the BC (or body force). One node is used as the "supernode" and other rows are lumped to this row. The other nodal dofs will get the same value as the one in the supernode. 


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@7062 04224531-1f84-46d8-96ce-875b9e37dce3
Test cases for constant valued BCs.


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@7063 04224531-1f84-46d8-96ce-875b9e37dce3