fix detection of UTF-16 BOM

http://community.sharpdevelop.net/forums/p/15627/39925.aspx#39925

src/Main/Base/Project/Src/Services/MimeTypeDetection.cs

@@ -25,7 +25,11 @@ namespace ICSharpCode.SharpDevelop
 		
 		static unsafe string FindMimeType(byte[] buffer, int offset, int length)
 		{
-			if (buffer.Length == 0)
+			if (buffer.Length == 0 ||
+				// UTF-16 Big Endian
+				(buffer.Length >= 2 && buffer[0] == 0xFE && buffer[1] == 0xFF) ||
+				// UTF-16 Little Endian
+				(buffer.Length >= 2 && buffer[0] == 0xFF && buffer[1] == 0xFE))
 				return "text/plain";
 			
 			fixed (byte *b = &buffer[offset]) {