Graph view option to crop runahead tasks.
Graph view: also crop tasks held beyond final cycle time.
gcylc back compat for new err log functionality.
More gcylc backward compatibility with 5.3.0 suites.
Merge branch 'master' into graph-view-runahead
Merge pull request #763 from hjoliver/graph-view-runahead

Graph view option to crop runahead tasks.