make ActionBuilder covariant

ActionBuilder is more flexible if it is declared to be covariant rather than invariant in its higher kinded type R.
R only appears in covariant positions ActionBuilder:
…(block: R[A] => Result):… is in a contravariant position and R[A] is the contravariant position of the function type, which overall makes R covariant.
Being covariant, ActionBuilder[WrappedRequest] (or other subtypes of WrappedRequest) can be safely upcast to ActionBuilder[Request].
Upgraded to SBT 0.13

* Actually upgraded to 0.13.1-RC2 to address
  https://github.com/sbt/sbt/issues/937
* Also had to upgrade to specs 2.3.1 to work around issue with scalaz
  pulling in Scala 2.10.1 and SBT not honouring our scala version
* Upgraded scalariform, which meant some files change formatting
* SBT runs forked tests in a different directory, changed the tests that
  failed as a result to hopefully be more resilient to working directory
  changes
* Implements #1643
* Also fixed #1710 - caching is now used for scala/javadoc compilation
quickfix for return type of the SimpleResult methods
Enabled some tracing in an attempt to diagnose the intermittent CI issue we’re now getting.
[#2001] Fix typo in welcome.scala.html
add spec for flash cookie
The main motivation for this change is that Bonecp connection tracking appears to closing a connection that has not been checked back in. See https://playframework2.ci.cloudbees.com/job/play2-master/1420/consoleFull and search for “disableConnectionTracking” and you’ll see that jdbc[4]’s connection is closed. Tracing back from there the connection for jdbc[4] does not appear to have been checked out (also verified by looking at the source code that should call the check in). It appears to me that the connection should remain open given that it is part of the pool.

Interestingly this problem is intermittent on master, doesn’t occur on the PR validation branch and I cannot reproduce it locally. Perhaps a race condition within BoneCP?

The secondary motivation to this change is that connections do not require management by BoneCP in a situation where they are being managed by a framework such as Play. The BoneCP management will add overhead so not requiring it by default may improve performance.
[#911] Prefix imports by _root_
Merge pull request #2009 from huntc/disableConnectionTracking

Enabled disableConnectionTracking option for Bonecp
Merge pull request #2003 from baloo/improvements/2001-welcome-typo

[#2001] Fix typo in welcome.scala.html
[#1787] Corrects apache Reverse Proxy Configuration
Upgrade of the native packager w.r.t. issue #1928
Merge pull request #1643 from jroper/1643-upgrade-013

Upgrade Play build to SBT 0.13
Merge pull request #2006 from yanns/flashSpec

add spec for flash cookie
Merge pull request #2016 from baloo/improvements/1787-Apache-RP

[#1787] Corrects apache Reverse Proxy Configuration
Merge pull request #1928 from huntc/native-pkg-update

JAVA_OPTS not honoured
Merge pull request #2010 from baloo/improvements/911-imports-utils-package

[#911] Prefix imports by _root_
Merge pull request #1996 from julienrf/fix/result-return-type

quickfix for return type of the SimpleResult methods #1996
Add ActionFunction, a generic version of ActionBuilder

Also includes some other useful refinements on ActionFunction: ActionRefiner,
ActionTransformer, and ActionFilter.  Proposal for issue #1986.
Update action composition documentation to describe ActionFunction

This replaces the previous section on different request types which manually
implemented ActionBuilders with roughly equivalent uses of ActionFunction.

Also reduced some headers to more clearly delineate the two sections (on
Actions and Builders).