[MPMD-206] Make the sourceDirectories configurable
I have changed the parameters so that they are not read-only any more.
However due to MNG-5440 you cannot yet set values for source directories in your own POM. Once a fix for that issue has been made to Maven core I will add an integration test for this issue, that will require at least that version of Maven to run. I have not committed the provided documentation changes yet. That will have to wait until it is actually possible to configure things that way.

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1687493 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/main/java/org/apache/maven/plugin/pmd/AbstractPmdReport.java b/src/main/java/org/apache/maven/plugin/pmd/AbstractPmdReport.java
index de5ceeb..0a3328d 100644
--- a/src/main/java/org/apache/maven/plugin/pmd/AbstractPmdReport.java
+++ b/src/main/java/org/apache/maven/plugin/pmd/AbstractPmdReport.java
@@ -128,13 +128,13 @@
     /**
      * The directories containing the sources to be compiled.
      */
-    @Parameter( property = "project.compileSourceRoots", required = true, readonly = true )
+    @Parameter( defaultValue = "${project.compileSourceRoots}" )
     private List<String> compileSourceRoots;
 
     /**
      * The directories containing the test-sources to be compiled.
      */
-    @Parameter( property = "project.testCompileSourceRoots", required = true, readonly = true )
+    @Parameter( defaultValue = "${project.testCompileSourceRoots}" )
     private List<String> testSourceRoots;
 
     /**