Regression introduce by pull-request #38 merge

[jfougere]

The modification done with the pull-request #38 makes the build failed when running tests.

Plugins classes are no more included in classpath when running maven-test goal.
Reverting changes made in this pull-request make the build and tests succeed.

Build was OK when using 2.3.4 maven plugin.

Below is the stack trace obtained with the official 2.3.7 maven plugin:

Fatal error forking Grails JVM: java.lang.reflect.InvocationTargetException
java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at org.grails.launcher.GrailsLauncher.launch(GrailsLauncher.java:150)
    at org.grails.maven.plugin.tools.ForkedGrailsRuntime.main(ForkedGrailsRuntime.java:168)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.grails.launcher.GrailsLauncher.launch(GrailsLauncher.java:144)
    ... 1 more
Caused by: java.lang.NoClassDefFoundError: KickstartResources
    at Config.run(Config.groovy:137)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
......
Caused by: java.lang.ClassNotFoundException: KickstartResources
    at org.grails.launcher.RootLoader.findClass(RootLoader.java:147)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
    at org.grails.launcher.RootLoader.loadClass(RootLoader.java:119)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
    ... 435 more

KickstartResources is a plugin class.