DatasetResource: use default toString() for setting attachment filename

Fix uwescience/myria-web#190
MasterCatalog: set query plan null if cannot deserialize it

Fix #600
Merge pull request #604 from uwescience/fix-myria-web-190

DatasetResource: use default toString() for setting attachment filename
Merge pull request #606 from uwescience/fix-600

MasterCatalog: set query plan null if cannot deserialize it
Update janino, allow default imports for expressions
remove unused const eval interface
Implement hash expression (md5 for now) operator as requested my @billhowe
Histogram query: be more efficient

Equivalent, but much more efficient, algorithm.
Fix comment
Merge pull request #609 from uwescience/dhalperi-improve-profiler

Histogram query: be more efficient
Merge branch 'master' into hash-expression
reinstate spacing
Merge pull request #608 from uwescience/hash-expression

Hash expression
Tuple: implement Cloneable

Deep copy of a Tuple
UserDefinedAggregate: improve efficiency by only compiling once

Previously, each aggregator recompiled the expressions into aggregators
to initialize, update, and finalize the aggregate state. Refactor the
code to compute all of these things once and then pass copies (or
references as appropriate) to the children.
build scripts: update coveralls plugin

See
https://github.com/kt3k/coveralls-gradle-plugin/blob/f3dcd0e0515b499baccdc9841cc545a1c1471b03/README.md
Merge pull request #611 from uwescience/fix-coveralls

build scripts: update coveralls plugin
Merge branch 'master' into uda-efficiency
Merge pull request #610 from uwescience/uda-efficiency

Refactor UDAs for dramatic efficiency boost
Merge branch 'master' into slxu-fix-network-backpressure