slick/slick — pull request #797 by tminglei (2014-05-04 06:02:18+00:00)
Title: add window functions support

This patch is adding **window function** support to `slick`.

A usage example of window function is as below:
```scala
salary.avg :: Over.partitionBy(dept).orderBy(dept,salary)
.rowsFrame(RowCursor.UnboundPreceding, RowCursor.CurrentRow)
```

Pls help review and give your suggestions.