Four new stable kernels

Greg Kroah-Hartman has announced the release of the 4.13.6, 4.9.55, 4.4.92, and 3.18.75 stable kernels. As usual, theycontain fixes throughout the tree, so users should upgrade.

Update: Kroah-Hartman released 4.9.56: "It fixes a networkingbug in 4.9.55. Don't use 4.9.55, it's busted, sorry about that, Ishould have held off and gotten more testing on it, my fault :("