Finagle, Ostrich, Util: Fix sbt project definition

Problem

Finagle was not compiling with sbt for multiple reasons:
- the java compilation of AbstractCloseAwaitably.java required one extra import
- finagle-httpx-compat required direct dependencies on finagle-http(x)

Solution

Fix the sbt project definition of Util/Finagle.
While I was there, I cleaned up some scaladoc warning in util and
some compilation warning in ostrich.

RB_ID=525909