Eigen detection bugfixes
Eigen detection bugfixes

We shouldn't rely on an inadequate Eigen.  This fixes both a caching
issue and an environment variable issue that could cause that to
happen.  We now fall back on contrib/ when necessary.

Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh