[MNG-2739] Adding validation logic to DefaultMavenTools and ProjectUtils, to make sure repositories have id and url before constructing an ArtifactRepository instance...this code is used ahead of normal model validation, so it needs to be included here. Also, introducing a new exception to handle the errors when these elements are missing.

Files:
modified: /maven/components/trunk/maven-model/src/main/mdo/maven.mdo (try)
modified: /maven/components/trunk/maven-project/src/main/java/org/apache/maven/project/DefaultMavenProjectBuilder.java (try)
modified: /maven/components/trunk/maven-project/src/main/java/org/apache/maven/project/error/ProjectErrorReporter.java (try)
modified: /maven/components/trunk/maven-project/src/main/java/org/apache/maven/MavenTools.java (try)
modified: /maven/components/trunk/maven-project/src/main/java/org/apache/maven/project/error/DefaultProjectErrorReporter.java (try)
modified: /maven/components/trunk/maven-project/src/main/aspect/org/apache/maven/project/aspect/PBEDerivativeReporterAspect.aj (try)
added: /maven/components/trunk/maven-project/src/main/java/org/apache/maven/project/MissingRepositoryElementException.java (try)
modified: /maven/components/trunk/maven-project/src/main/java/org/apache/maven/DefaultMavenTools.java (try)
modified: /maven/components/trunk/maven-project/src/main/java/org/apache/maven/project/ProjectUtils.java (try)