Merge branch 'stitch_mesh' of https://github.com/jwpeterson/libmesh

This branch optimizes SerialMesh::stitch_meshes.
Merge branch 'stitch_mesh' of https://github.com/jwpeterson/libmesh

John updated the branch to pass the tolerance down.
Merge branch 'master' of github.com:libMesh/libmesh

Merging master.
Merge branch 'master' of github.com:libMesh/libmesh
Merge branch 'master' of github.com:libMesh/libmesh