Removed the remaining expect methods from IvyHttpModule.
Added ModuleVersionMetaData.artifact() that accepts type, ext and classifier attributes, and use this in a few places instead of creating an Ivy DefaultArtifact.
Use a Set instead of an Iterable.
Changed DefaultModuleVersionArtifactIdentifier so that it no longer requires a ModuleVersionIdentifier.
More tweaks to performance test thresholds.