fix #1085. Manually applied 268c9040d5. Thanks Jason for the tip!

The patch is part of rails 2.3.6, so it will be included when we upgrade to 2.3.9

vendor/rails/railties/lib/rails/gem_dependency.rb

@@ -83,7 +83,7 @@ module Rails
       specification.dependencies.reject do |dependency|
         dependency.type == :development
       end.map do |dependency|
-        GemDependency.new(dependency.name, :requirement => dependency.version_requirements)
+        GemDependency.new(dependency.name, :requirement => (dependency.respond_to?(:requirement) ? dependency.requirement : dependency.version_requirements))
       end
     end
 
@@ -115,9 +115,16 @@ module Rails
       @spec = s
     end
 
-    def requirement
-      r = version_requirements
-      (r == Gem::Requirement.default) ? nil : r
+    if method_defined?(:requirement)
+      def requirement
+        req = super
+        req unless req == Gem::Requirement.default
+      end
+    else
+      def requirement
+        req = version_requirements
+        req unless req == Gem::Requirement.default
+      end
     end
 
     def built?