Prepare build for inclusion of java8-compat

<h1>Allow mixed builds in ant</h1>

The `JFunction` classes depend on the `FunctionN` traits, so the
Java compiler needs the Scala library on the classpath.

At the same time, while compiling the Scala library, the symbols for
`JFunction` classes need to be available to emit indy-lambda closures.
Therefore we pass the `JFunctions` as Java sources while compiling the
Scala library.

<h1>Upgrade versions of osgi tools</h1>

Set the required java version in bnd files (JavaSE-1.8).

Introduce `scala-swing.version.osgi` as a quick hack to
allow manually deriving an osgi-friendly version number
for the `scala-swing.version.number`. The latter is used
to resolve the artifact, the osgi version is just so we
can generate a bundle that osgi will accept.

Bnd 1.50 doesn't work with Java 8 classfiles, so upgrade to 2.4.1.

Also upgrade all other tools to make tests pass.
For `org.eclipse.osgi` we moved to the group ID `org.eclipse.tycho`,
where there's a newer version available. The osgi tests would fail
with the most recent version available in the `org.eclipse.osgi` groupID.

The new version of bnd only copies *classfiles* from the
original into the resulting jar, while the old version also copied
all other files. This caused osgi test failure with a `NoClassDefFound`,
which was really due to a `NumberFormatException` in `ScalaVersion`,
as it couldn't find the properties file to parse the version in...

Include resources from source jar into osgi bundle as follows:
```
  Include-Resource: @@SOURCE_JARNAME@
```

This makes bnd copy all resources from the source jar. I ran the
following on the osgi artifacts of this branch, and on 2.11.x:

```
for f in `find build/osgi -name '*.jar' -a -not -name '*src.jar'`; do unzip -l $f | grep -v '\.class' ; done
```

Comparing the two file lists, things look OK:
https://gist.github.com/lrytz/be08db051a53eded192d

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