Fix ./build/<stage>/bin/scaladoc

Was:

    ./build/quick/bin/scaladoc -version
    Exception in thread "main" java.lang.NoClassDefFoundError: scala/tools/nsc/ScalaDoc
    Caused by: java.lang.ClassNotFoundException: scala.tools.nsc.ScalaDoc

Now:

    % for tool in ./build/quick/bin/{fsc,scala,scalac,scaladoc,scalap}; do $tool -version; done
    Fast Scala compiler version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scala code runner version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scala compiler version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scaladoc version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scala classfile decoder version 2.0.1 -- (c) 2002-2013 LAMP/EPFL

Review by @gkossakowski