[Installer] Handle build configuration case insensitively

lib/cocoapods/installer.rb

@@ -96,7 +96,7 @@ module Pod
     def resolve_dependencies
       UI.section "Analyzing dependencies" do
         analyze
-        validate_whitelisted_configurations
+        validate_build_configurations
         prepare_for_legacy_compatibility
         clean_sandbox
       end
@@ -183,11 +183,11 @@ module Pod
     #
     # @raise  If a unknown user configuration is found.
     #
-    def validate_whitelisted_configurations
+    def validate_build_configurations
       whitelisted_configs = pod_targets.map do |target|
         target.target_definition.all_whitelisted_configurations
       end.flatten.uniq
-      all_user_configurations = analysis_result.all_user_build_configurations.keys
+      all_user_configurations = analysis_result.all_user_build_configurations.keys.map(&:downcase)
 
       remainder = whitelisted_configs - all_user_configurations
       unless remainder.empty?

lib/cocoapods/installer/user_project_integrator/target_integrator.rb

@@ -112,7 +112,6 @@ module Pod
             native_target.build_configurations.each do |config|
               path = target.xcconfig_relative_path(config.name)
               xcconfig = user_project.files.select { |f| f.path == path }.first || user_project.new_file(path)
-
               check_overridden_build_settings(target.xcconfigs[config.name], native_target)
               config.base_configuration_reference = xcconfig
             end

spec/unit/installer_spec.rb

@@ -154,7 +154,7 @@ module Pod
           target_definition.whitelist_pod_for_configuration('JSONKit', 'YOLO')
           @installer.send(:analyze)
           should.raise Informative do
-            @installer.send(:validate_whitelisted_configurations)
+            @installer.send(:validate_build_configurations)
           end
         end
 
@@ -163,7 +163,7 @@ module Pod
           target_definition.whitelist_pod_for_configuration('JSONKit', 'Test')
           @installer.send(:analyze)
           should.not.raise do
-            @installer.send(:validate_whitelisted_configurations)
+            @installer.send(:validate_build_configurations)
           end
         end
       end