Source dependencies + Install fix

Hi,

there is an issue with downloading validation-api source dependencies at least on grails 2.2.x (I have not checked under other 2.x versions). The jar is not fetched at all using the current resolving mechanism and think the problem is connected with GRAILS-6147 issue. However, I think I have managed to fix it - I use now m:classifier attribute to specify classifier and an additional line is needed in BuildConfig under grails.project.dependency.resolution:

dependencyManager.ivySettings.defaultCacheIvyPattern = "[organisation]/[module](/[branch])/ivy-[revision](-[classifier]).xml"

besides this, this branch contains another fix, for the effect I got once: _Install script failed at updatingClasspath. Therefore, I have wrapped it in a try-catch block. Updating the classpath directly during the installation is only important if you triggered this by compile task or some other depending on it. Otherwise, it could be avoided as well. Meantime I refresh first my dependencies via grails refresh-dependencies before starting any compilation - it is somehow safer.