Allows EIGEN_STACK_ALLOCATION_LIMIT to be 0 for no limit
Add explanations of the logic behind the matrix-vector products
Fix compilation with ICC/MSVC combo
BDCSVD: Use HouseholderSeq directly.

--HG--
extra : transplant_source : _%13%EB%FAO%AA%8E%C4%18%DE%D8%18%AA%975W%C3%A8%B0%93