ProjectChangeWatcher should respect "DetectExternalChanges" setting value

src/Main/Base/Project/Src/Project/ProjectChangeWatcher.cs

@@ -100,7 +100,8 @@ namespace ICSharpCode.SharpDevelop.Project
 
 			if (!enabled || FileChangeWatcher.AllChangeWatchersDisabled)
 				return;
-
+			if (!FileChangeWatcher.DetectExternalChangesOption)
+				return;
 			if (string.IsNullOrEmpty(fileName))
 				return;
 			if (FileUtility.IsUrl(fileName))

src/Main/Base/Project/Workbench/FileChangeWatcher.cs

@@ -132,7 +132,7 @@ namespace ICSharpCode.SharpDevelop.Workbench
 				return;
 			if (globalDisableCount > 0)
 				return;
-			if (DetectExternalChangesOption == false)
+			if (!DetectExternalChangesOption)
 				return;
 			
 			string fileName = file.FileName;