Bug#867648: jruby-maven-plugins: FTBFS: RailsService.java:[26, 20] variable session might not have been initialized

[Emmanuel Bourg]

The build currently fails with another error:

[INFO] --- exec-maven-plugin:1.6.0:exec (install gems) @ ruby-tools ---
LoadError: no such file to load -- rubygems/installer
  require at org/jruby/RubyKernel.java:961
   <main> at /build/jruby-maven-plugins-1.1.5+ds1/ruby-tools/src/main/scripts/install_gems.rb:1
[ERROR] Command execution failed.
org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
    at org.apache.commons.exec.DefaultExecutor.executeInternal (DefaultExecutor.java:404)
    at org.apache.commons.exec.DefaultExecutor.execute (DefaultExecutor.java:166)
    at org.codehaus.mojo.exec.ExecMojo.executeCommandLine (ExecMojo.java:804)
    at org.codehaus.mojo.exec.ExecMojo.executeCommandLine (ExecMojo.java:751)
    at org.codehaus.mojo.exec.ExecMojo.execute (ExecMojo.java:313)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:134)