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
Updating github traffic.
update derived Makefile.in
removing eigen 3.2.0
Missing restart files suck; test in opt mode too

"Fun" fact: although EquationSystems::read() correctly errors out when
asked to read a non-existent xdr file, in opt mode it could keep right
on executing when asked to read a non-existent xda file, which seemed
to behave like a no-op.
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
Updating github traffic statistics.
Updating references.
* Vavourakis, 2014.
* Nagler, 2014.
Updating citation plot and web page.
Updating statistics for March 2014.
Fixing legend on 'downloads' plot.
Updating web statistics plot files.
Write Tecplot header based on the dimension of the actual elements in
the Mesh, rather than mesh.mesh_dimension().
Factor out logical element dimension checking into a separate function
so it can be used in both the ASCII and binary writers.
Use elem_dimension instead of Mesh dimension in the binary Tecplot writer.
Add ability to search for X11 header files in different locations,
and pass this path down to the TECIO Makefile.