Small fixes to explicit Runge-Kutta scheme.


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6979 04224531-1f84-46d8-96ce-875b9e37dce3
Enable lumped matrix & explicit in time solution in parallel.


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6980 04224531-1f84-46d8-96ce-875b9e37dce3