Cross-build to Scala 2.11

I have changed the build to cross-compile to Scala `2.11.0-RC1`. The project compiles (obviously with some deprecation warnings in `2.11`), but there are a couple of tests that fail, so this is work in progress. We have yet to look into it, maybe the way to deal with it is to have a separate branch for 2.10.

One:
```
[info] - disable any2stringadd *** FAILED ***
[info]   result.errors
[info]   Expected List("Scala inserted an any2stringadd call"), but got List() (Any2StringAddTest.scala:13)
```

Two:
```
[info] UnsafeTest:
[info] - can't use `null`, `var`, non-unit statements, Option#get, LeftProjection#get, RightProjection#get, or any2stringadd *** FAILED ***
[info]   result.errors
[info]   Expected List("Inferred type containing Any", "Inferred type containing Any", "Scala inserted an any2stringadd call", "LeftProjection#get is disabled - use LeftProjection#toOption instead", "RightProjection#get is disabled - use RightProjection#toOption instead", "LeftProjection#get is disabled - use LeftProjection#toOption instead", "RightProjection#get is disabled - use RightProjection#toOption instead", "Statements must return Unit", "null is disabled", "Option#get is disabled - use Option#fold instead", "var is disabled"),
          but got List("Inferred type containing Any", "Inferred type containing Any", "LeftProjection#get is disabled - use LeftProjection#toOption instead", "RightProjection#get is disabled - use RightProjection#toOption instead", "LeftProjection#get is disabled - use LeftProjection#toOption instead", "RightProjection#get is disabled - use RightProjection#toOption instead", "Statements must return Unit", "null is disabled", "Option#get is disabled - use Option#fold instead", "var is disabled") (UnsafeTest.scala:31)
```