Additional options for Ivy resolvers.

Specify an Ivy resolver with ", descriptorOptional" to make Ivy
descriptor files optional for that repository or with
", skipConsistencyCheck" to disable Ivy consistency checks for
that repository.

launch/interface/src/main/java/xsbti/IvyRepository.java

@@ -9,4 +9,6 @@ public interface IvyRepository extends Repository
 	String ivyPattern();
 	String artifactPattern();
 	boolean mavenCompatible();
+	boolean skipConsistencyCheck();
+	boolean descriptorOptional();
 }