Removed some obsolete imports from dbchooser.
Merge branch 'master' of github.com:cylc/cylc
Avoid unnecessary dependence graphviz.

Suites can now run, and gcylc can be used (minus the graph view) if
graphviz/pygraphviz is not installed.
Updated the change log.
Plot naked dummy tasks in namespace graphs.

Closes #338.
Merge pull request #354 from hjoliver/338-graph-naked-dummy-tasks

Plot naked dummy tasks in namespace graphs.
Merge pull request #352 from hjoliver/347-dependence-on-graphviz

Fixes #347 - dependence on graphviz