Avoid false positive SLEPc detection

If we seem to have SLEPc, but there's some reason we can't scarf build
configuration from SLEPc, then we really don't have SLEPc.

I got caught by this when trying a new PETSC_ARCH for which I hadn't
yet built SLEPc.
Eigen 3.2.1 source
update symlink
update derived Makefile.in
removing eigen 3.2.0
Merge pull request #207 from libMesh/slepc_failure

Avoid false positive SLEPc detection
Merge pull request #218 from benkirk/eigen_refresh

Eigen refresh to v3.2.1
reduced_basis_ex2 fails in parallel