Homebrew CVS is required for Xcode 5+

Library/Homebrew/dependency_collector.rb

@@ -166,7 +166,7 @@ class DependencyCollector
     when strategy <= BazaarDownloadStrategy
       Dependency.new("bazaar", tags)
     when strategy <= CVSDownloadStrategy
-      Dependency.new("cvs", tags) if MacOS.version >= :mavericks
+      Dependency.new("cvs", tags) unless MacOS::Xcode.provides_cvs?
     when strategy < AbstractDownloadStrategy
       # allow unknown strategies to pass through
     else

Library/Homebrew/os/mac/xcode.rb

@@ -150,6 +150,10 @@ module OS
         version < "4.3"
       end
 
+      def provides_cvs?
+        version < "5.0"
+      end
+
       def default_prefix?
         if version < "4.3"
           %r{^/Developer} === prefix