[Fix] Do not quote `$(inherited)`. Fixes #956.

lib/cocoapods/generator/xcconfig.rb

@@ -147,7 +147,7 @@ module Pod
       # @todo   Inheritance should be properly handled in Xcconfigs.
       #
       DEVELOPER_FRAMEWORKS_SEARCH_PATHS = [
-        '"$(inherited)"',
+        '$(inherited)',
         '"$(SDKROOT)/Developer/Library/Frameworks"',
         '"$(DEVELOPER_LIBRARY_DIR)/Frameworks"'
       ]

spec/unit/generator/xcconfig_spec.rb

@@ -102,7 +102,7 @@ module Pod
       spec.xcconfig = { 'OTHER_LDFLAGS' => '-no_compact_unwind' }
       spec.frameworks = ['SenTestingKit']
       xcconfig = generator.generate
-      xcconfig.to_hash['FRAMEWORK_SEARCH_PATHS'].should == '"$(inherited)" "$(SDKROOT)/Developer/Library/Frameworks" "$(DEVELOPER_LIBRARY_DIR)/Frameworks"'
+      xcconfig.to_hash['FRAMEWORK_SEARCH_PATHS'].should == '$(inherited) "$(SDKROOT)/Developer/Library/Frameworks" "$(DEVELOPER_LIBRARY_DIR)/Frameworks"'
     end
 
     it "doesn't include the developer frameworks if already present" do
@@ -112,7 +112,7 @@ module Pod
       generator = Generator::XCConfig.new(config.sandbox, [consumer_1, consumer_2], './Pods')
       spec.frameworks = ['SenTestingKit']
       xcconfig = generator.generate
-      xcconfig.to_hash['FRAMEWORK_SEARCH_PATHS'].should == '"$(inherited)" "$(SDKROOT)/Developer/Library/Frameworks" "$(DEVELOPER_LIBRARY_DIR)/Frameworks"'
+      xcconfig.to_hash['FRAMEWORK_SEARCH_PATHS'].should == '$(inherited) "$(SDKROOT)/Developer/Library/Frameworks" "$(DEVELOPER_LIBRARY_DIR)/Frameworks"'
     end
 
     #-----------------------------------------------------------------------#