Avoid duplicates in vcs roots

The project is often a module, i.e. its root is added as project base dir.
=> check for duplicates when adding a content root.

platform/lang-impl/src/com/intellij/openapi/vcs/impl/ModuleDefaultVcsRootPolicy.java

@@ -86,7 +86,7 @@ public class ModuleDefaultVcsRootPolicy extends DefaultVcsRootPolicy {
         // explicitly (we know it anyway)
         VcsDirectoryMapping mapping = mappingList.getMappingFor(file, module);
         final String mappingVcs = mapping != null ? mapping.getVcs() : null;
-        if (vcsName.equals(mappingVcs)) {
+        if (vcsName.equals(mappingVcs) && !result.contains(file)) {
           result.add(file);
         }
       }