removed warning. Added size_type to Eigen::DenseBase in order to appropriately type loops. This helps with comparing unsigned vs signed quantities.
removed warning. Added size_type to Eigen::DenseBase in order to appropriately type loops. This helps with comparing unsigned vs signed quantities.

git-svn-id: e699fe4639e7715a7f788fcbdac464b34c416b62@748 9a304bd9-dce1-f7c0-8d5c-bb1642157d4e

stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math