Lock-down specific Scala revision for now

So I can easily test dbuild configuration without rebuilding everything
from scratch due to new Scala revision being pulled in.
Add .gitignore file.
Add Play-core to dbuild.

And first of its dependencies: scala-io and scala-arm. It doesn't build
yet.
Merge remote-tracking branch 'retronym/jenkins' into jenkins
Add scala-continuations that is neded by scala-arm
Switch to my own fork of scala-arm

My branch changes how arm depends on the continuations plugin.
Build just core and file subprojects from scala-io.

Only those two are needed by downstream (Play) projects.
Switch to my own fork of Play

Which adds dependency on scala-xml that is required in Scala 2.11 if
you use xml api.
Switch to my own fork of scala-io.

My fork:
  1. disables building of scaladoc docs (due to regression in scaladoc)
  2. adds dependency on scala-parser-combinators
Lock particular version of specs2

Latest master of specs2 breaks on Scala master due to
https://github.com/etorreborre/specs2/commit/2f4aca25c66e1f5640b32642208178d46888dfec
Bump Scala version to latest master.
Add work-around for duplicated source files in Play build.

For reason I don't really understand, PlayVersion.scala is being passed
twice to scalac when compiling Play2-core with dbuild. Let's work around
it for now until I can understand what's going on.
Update to sbt 0.13.1 in scala-io

My fork switched to sbt 0.13.1. Let's mention this.
Work-arounds for compiling scala-io.

Add work-around for scala compiler crash described in SI-8306. Also,
do not run tests because one of them fails for some reason.
Update to latest scala master.
Merge remote-tracking branch 'retronym/jenkins' into play

Conflicts:
	community-2.11.x.dbuild
Switch back to tracking scala master.
Merge pull request #4 from gkossakowski/play

Add Play2-core