SI-7201 scaladoc url in scala-(library,actors,swing,reflect) pom

The project/properties/info.apiURL pom property is used by SBT
to link to an artifact's scaladoc.

For scala library version $v, the url is http://www.scala-lang.org/api/$v/
Note that actors, reflect and swing are included in the library docs in 2.10.x.
Merge pull request #2540 from adriaanm/ticket-7201

SI-7201 scala-library's pom points to scaladoc url