handle Read from non-trivial path in workflow builder
Convert WorkflowPhase from PhaseE to Phase.

So we can collect errors whenever a node can’t be created, but only report them if we don’t have a Workflow at the end.
Convert JsExprPhase from PhaseE.
Convert SelectorPhase from PhaseE.
Convert FieldPhase from PhaseE.
Add a test for filter that requires JS.
Merge pull request #256 from mossprescott/paths-quick-fix

handle Read from non-trivial path in workflow builder
Add test for mixing JS and non-JS filter.
Merge remote-tracking branch 'upstream/master' into joins

Conflicts:
	src/main/scala/slamdata/engine/physical/mongodb/planner.scala
Merge pull request #257 from sellout/joins

arbitrary JS in filters
Fix JS output for MapReduce.
Complete WorkflowOp map.
Add a join test.
[minor] Formatting cleanup.
fix indent in generated JS
handle MapReduceTask in RenderTree
also a RenderTree[Js] instance
ignore ^D in REPL ('exit' still works)
Merge pull request #259 from sellout/joins

Joins
fix white space in tests
Merge pull request #260 from mossprescott/misc

A handful of small fixes