[Resolver] Process target definitions in the specification order.

Related to #899

lib/cocoapods/resolver.rb

@@ -58,7 +58,7 @@ def resolve
       @cached_specs    = {}
       @specs_by_target = {}
 
-      target_definitions = podfile.target_definitions.values.sort_by{ |td| td.name.to_s }
+      target_definitions = podfile.target_definition_list
       target_definitions.each do |target|
         UI.section "Resolving dependencies for target `#{target.name}' (#{target.platform})" do
           @loaded_specs = []