Enable syntax highlighting for .master files.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/Resources/ASPX.xshd

@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <!-- converted to AvalonEdit format by Siegfried Pammer in 2010 -->
-<SyntaxDefinition name="ASP/XHTML" extensions=".asp;.aspx;.asax;.asmx" xmlns="http://icsharpcode.net/sharpdevelop/syntaxdefinition/2008">
+<SyntaxDefinition name="ASP/XHTML" extensions=".asp;.aspx;.asax;.asmx;.master" xmlns="http://icsharpcode.net/sharpdevelop/syntaxdefinition/2008">
 	<Color name="ASPSectionStartEndTags" foreground="Black" background="Yellow" exampleText="&lt;% System.Console.WriteLine(&quot;Hello World!&quot;); %&gt;" /> 
 	<Color name="ASPSection" foreground="Black" background="#FFF7F2E3" exampleText="&lt;% System.Console.WriteLine(&quot;Hello World!&quot;); %&gt;" />
 	<RuleSet ignoreCase="true">

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/Resources/Resources.cs

@@ -25,7 +25,7 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 			
 			hlm.RegisterHighlighting("JavaScript", new[] { ".js" }, "JavaScript-Mode.xshd");
 			hlm.RegisterHighlighting("HTML", new[] { ".htm", ".html" }, "HTML-Mode.xshd");
-			hlm.RegisterHighlighting("ASP/XHTML", new[] { ".asp", ".aspx", ".asax", ".asmx" }, "ASPX.xshd");
+			hlm.RegisterHighlighting("ASP/XHTML", new[] { ".asp", ".aspx", ".asax", ".asmx", ".master" }, "ASPX.xshd");
 			
 			hlm.RegisterHighlighting("Boo", new[] { ".boo" }, "Boo.xshd");
 			hlm.RegisterHighlighting("Coco", new[] { ".atg" }, "Coco-Mode.xshd");