better toString for LogicalPlan and Data
improved debug logging

RenderTree instances for WorkflowBuilder, WorkflowOp

fix grouped value node type

fix toString() for DocVar.ROOT()

clean up tree rendering for Group and Reshape

use round box glyph
rename test/data files
implement DISTINCT as query modifier and as unary operator (Fixes #211)
Merge pull request #317 from mossprescott/minor

don't delete collections prefixed with "Slam"
update stages
additional tests
delete commented code
new type for distinct flag
ignore lbase and rbase coming in from caller
eliminate lbase and rbase params; some cleanup
in progress
remove the problematic special case; mark test pending; some cleanup
Merge branch 'master' into ready/211
Merge pull request #285 from mossprescott/ready/211

Handle common cases for DISTINCT
improved pipeline/workflow rendertree node types and labels