fix #320 An error occurred : C# Ambience does not escape parameter names

src/Libraries/NRefactory/ICSharpCode.NRefactory.CSharp/OutputVisitor/InsertRequiredSpacesDecorator.cs

@@ -56,7 +56,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		
 		public override void WriteIdentifier(Identifier identifier)
 		{
-			if (identifier.IsVerbatim) {
+			if (identifier.IsVerbatim || CSharpOutputVisitor.IsKeyword(identifier.Name, identifier)) {
 				if (lastWritten == LastWritten.KeywordOrIdentifier) {
 					// this space is not strictly required, so we call Space()
 					Space();

src/Libraries/NRefactory/ICSharpCode.NRefactory.CSharp/OutputVisitor/TextWriterOutputFormatter.cs

@@ -58,7 +58,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		public override void WriteIdentifier(Identifier identifier)
 		{
 			WriteIndentation();
-			if (identifier.IsVerbatim) {
+			if (identifier.IsVerbatim || CSharpOutputVisitor.IsKeyword(identifier.Name, identifier)) {
 				textWriter.Write('@');
 				column++;
 			}

src/Libraries/NRefactory/ICSharpCode.NRefactory.CSharp/Refactoring/TypeSystemAstBuilder.cs

@@ -806,6 +806,8 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 		{
 			MethodDeclaration decl = new MethodDeclaration();
 			decl.Modifiers = GetMemberModifiers(method);
+			if (method.IsAsync)
+				decl.Modifiers |= Modifiers.Async;
 			decl.ReturnType = ConvertType(method.ReturnType);
 			decl.Name = method.Name;