eigen 3.2.1->3.2.2

Bump bundled Eigen to latest release.

According to http://eigen.tuxfamily.org/index.php?title=Main_Page,

Eigen 3.2.2 has been released on August 4, 2014.

This is a maintenance release with many bug fixes since the release of 3.2.1 five months ago. In particular, this release includes various numerical improvements in JacobiSVD, LDLT, BiCGSTAB, and ColPivHouseholderQR. There are also some limited performance improvements and added functionality in the 3.2.2 release