[CodeIssues] Be more allowing when picking format string arguments in FormatStringIssue.

ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/FormatStringIssue.cs

@@ -126,7 +126,7 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 					if (parameter.Type.Equals(stringType) && parameterNames.Contains(parameter.Name) && argument is PrimitiveExpression) {
 						format = (string)((PrimitiveExpression)argument).Value;
 						formatStart = argument.StartLocation;
-					} else if (parameter.IsParams || parameter.Type.Equals(objectType)) {
+					} else if (format != null || parameter.IsParams) {
 						arguments.Add(argument);
 					}
 				}

ICSharpCode.NRefactory.Tests/CSharp/CodeIssues/FormatStringTests.cs

@@ -48,6 +48,27 @@ class TestClass
 			var issues = GetIssues (new FormatStringIssue (), input, out context);
 			Assert.AreEqual (1, issues.Count);
 		}
+		
+		[Test]
+		public void SupportsFixedArguments()
+		{
+			var input = @"
+class TestClass
+{
+	void Foo()
+	{
+		Bar(""{0}"", 1);
+	}
+
+	void Bar(string format, string arg0)
+	{
+	}
+}";
+			
+			TestRefactoringContext context;
+			var issues = GetIssues (new FormatStringIssue (), input, out context);
+			Assert.AreEqual (0, issues.Count);
+		}
 
 		[Test]
 		public void FormatItemIndexOutOfRangeOfArguments()