[nomaster] SI-7862: MANIFEST.MF file for Scala sources

In order to be able to use published Scala jars as OSGi bundles in the
Eclipse build, Eclipse needs to match sources and binaries. That is
done by making source jars *source bundles*. This PR adds the required
manifest entries. Nothing else should be affected (file names remain
the same).

Cherry picked from 655b7d2601d7db9e98bb405da0a67c9068c98626

Conflicts:
	build.xml

After this commit:

```
% ant -q dist.src
% for f in dists/scala-2.10.3-20130921-144112-892aa93cf7/src/*.jar; do \
    echo $f                                                            \
    unzip -p $f META-INF/MANIFEST.MF                                   \
  done

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/fjbg-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/msil-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/scala-actors-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)
Bundle-Name: Scala Actors Sources
Bundle-SymbolicName: org.scala-lang.scala-actors.source
Bundle-Version: 2.10.3.v20130921-144112-892aa93cf7
Eclipse-SourceBundle: org.scala-lang.scala-actors;version="2.10.3.v201
 30921-144112-892aa93cf7";roots:="."

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/scala-compiler-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)
Bundle-Name: Scala Compiler Sources
Bundle-SymbolicName: org.scala-lang.scala-compiler.source
Bundle-Version: 2.10.3.v20130921-144112-892aa93cf7
Eclipse-SourceBundle: org.scala-lang.scala-compiler;version="2.10.3.v2
 0130921-144112-892aa93cf7";roots:="."

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/scala-library-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)
Bundle-Name: Scala Library Sources
Bundle-SymbolicName: org.scala-lang.scala-library.source
Bundle-Version: 2.10.3.v20130921-144112-892aa93cf7
Eclipse-SourceBundle: org.scala-lang.scala-library;version="2.10.3.v20
 130921-144112-892aa93cf7";roots:="."

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/scala-partest-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/scala-reflect-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)
Bundle-Name: Scala Reflect Sources
Bundle-SymbolicName: org.scala-lang.scala-reflect.source
Bundle-Version: 2.10.3.v20130921-144112-892aa93cf7
Eclipse-SourceBundle: org.scala-lang.scala-reflect;version="2.10.3.v20
 130921-144112-892aa93cf7";roots:="."

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/scala-swing-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)
Bundle-Name: Scala Swing Sources
Bundle-SymbolicName: org.scala-lang.scala-swing.source
Bundle-Version: 2.10.3.v20130921-144112-892aa93cf7
Eclipse-SourceBundle: org.scala-lang.scala-swing;version="2.10.3.v2013
 0921-144112-892aa93cf7";roots:="."

dists/scala-2.10.3-20130921-144112-892aa93cf7/src/scalap-src.jar
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.4
Created-By: 1.6.0_37-b06-434-11M4509 (Apple Inc.)
```
Merge pull request #2976 from retronym/backport/7862

[nomaster] SI-7862: MANIFEST.MF file for Scala sources