Remove targets argument to internal methods.  Reorder targets according to MPI rank order.
Fixes comment.
Adds basic test for contexts' target attribute.
Remove target_to_rank, rank_to_target attributes on context.

Also fixes some typos; updates tests.
Resolved merge conflicts with master.
Merge branch 'master' into bugfix/resolve-target-rank-mapping
Merge pull request #210 from enthought/bugfix/resolve-target-rank-mapping

Fix context.targets attribute