fix grouping on expressions (Fixes #515)

- remove spurious rewriting of the source in groupBy
- simplify expr3 with at least one literal argument
- pending test for a trickier case
respond to PR feedback
- add planner test for the specific query mentioned in #515
- remove irrelevant order by in regresssion test
Merge pull request #522 from mossprescott/ready/515

fix grouping with expression in key(s)
clean up mongo-related junk in build log

- pipe mongodb output to /dev/null
- disable curl progress indicator
- turn off tar verbose output
Merge pull request #523 from mossprescott/minor

clean up mongo-related junk in build log
build correct workflow for groupby with JS (Fixes #469)

Avoid creating GroupBuilders on top of ExprBuilders, and conversely
favor making ExprBuilders over modifying the base in
ShapePreservingBuilders. This fixes all the cases covered by the
existing scalacheck test.

Added a pending test for queries with filtering, some of which are
still not working right (see #524).

Now simplifying JsCore that was generated by collapsing some of these
cases—specifically selecting a field from an object literal where the
keys is a constant.

Fixed an infinite loop in fixplate.

Improved RenderTree instances for \/ and These: no more blank nodes;
use nodeType, not label.
integration test for filtering with grouping by a JS expr

Slightly improved failure messages for containsAtLeast and containsExactly
Merge pull request #525 from mossprescott/ready/469

build correct workflow for groupby with JS (Fixes #469)