fix code generated for IfNull
implement date_part/Extract in JS (Fixes #380)

For use in filtering.

Not all fields currently implemented (see #399).
Merge pull request #400 from mossprescott/ready/380

implement date_part/Extract in JS; fix ifNull/Coalesce
don't rename source collections

If no temp collection is created for a query, the path to the source
collection is returned (even if the query came with a requested
destination).
Merge pull request #401 from mossprescott/hotfix/preserve-source-collections

don't rename source collections
bump version to 1.0.2-SNAPSHOT