Adds read and writable partitioned versions of TextLine and
TypeDelimited sources.
Add the Execution Monad
Get the tmp directory from the config
Add some tests
Generalize handling of merged TypedPipes
Add more zip methods and .unit to ease composition
Add Jco's writeThrough
Add Ian's suggested comment
Rename snapshotExecution to forceToDiskExecution for consistency
Merge pull request #975 from twitter/fix_typed_merge

Generalize handling of merged TypedPipes
Merge with develop
Add Kmeans test to execution
Merge pull request #974 from twitter/execution_monad

Make an Execution[T] type, which is a monad, which makes composing Jobs easy.
Fixes comment.
Write tests for typed partitioned sources.
JsonLine: allow read transformation to get correct fields in sourceTap

JsonLine previously did not have the transformations enabled
during the test phase (transformInTest set to false).

Because of this the only way to use the JsonLine was to create
a sub-class and override the transformInTest method with a ‘true’ def
value: as JsonLine can be effectively used with JobTest only
with transformation enabled, sub-classing and overriding was 
quite common.

When using JsonLine without conversation enabled you get a 
Cascading mapping exception:
“could not select fields: ... from: [{2}:'offset', 'line’]”

Default setting for transformInTest is kept to false for backward
compatibility with 0.9.x and 0.10.x.
Merge pull request #969 from CommBank/partitioned_sources

Read and writable partitioned sources
Merge pull request #971 from lucamilanesio/develop

JsonLine: enable read transformation in test to get correct fields in sourceTap