included jfreechart sources break scala_project

[Fabian Huch]

The recently updated jfreechart component (added in cc6e160130ab) breaks 
scala_project: Including the java sources via build.props is bad, since 
transitive dependencies (javax.servlet:servlet-api) are missing. This 
makes the generated scala_project no longer build properly (and thus 
IntelliJ IDEA cannot understand our Isabelle/Scala sources).


Fabian