Meta packages don't need versions

lib/rip/installer.rb

@@ -30,7 +30,7 @@ def install(package, parent = nil)
           return if installed
           @installed[package.name] = package
 
-          if !package.version
+          if !package.meta_package? && !package.version
             ui.abort "can't install #{package} - it has no version"
           end
 

lib/rip/package.rb

@@ -55,7 +55,7 @@ def self.for(source, *args)
     end
 
     def to_s
-      "#{name} (#{version})"
+      version ? "#{name} (#{version})" : name.to_s
     end
 
     memoize :cache_name

lib/rip/packages/ripfile_package.rb

@@ -15,6 +15,10 @@ def name
       source.split('/').last
     end
 
+    def version
+      nil
+    end
+
     def meta_package?
       true
     end