Added C interface for generalized eigen problem
Extended the functionality of test.c to check generalized eigenproblem,
both with and without already decomposed matrix

both fortran and C tests generated in generate_automake_test_programs.py
linker flags added by hand -- FIX this

We got reports from a user that there were troubles with certain domain
decompositions. So far the tests only looked at (approximately) square
decompositions in column-major process order.

Now, a new class of tests loops over all possible decompositions
(row * col) for a given number of total tasks.

So far, we can not confirm that there are any problems, all
possibilities work as expected.

The public "solve" method has been renamed "eigenvectors" since it
computes the eigenvalues and (at least parts of) the eigenvectors

Another routine "eigenvalues" will just compute the eigenvalues