ElasticSolve: Fixing principal strain computation

git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6948 04224531-1f84-46d8-96ce-875b9e37dce3
Update ParallelEigenSolve() to use ParallelIter(), with all its options, instead
of the internal BiCGStabEigen- routine.


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6949 04224531-1f84-46d8-96ce-875b9e37dce3