[Misc] Remove some extra string allocations.

Author: Therzok

Mono.Addins.Gui/Mono.Addins.Gui/AddinTreeWidget.cs

@@ -352,7 +352,7 @@ string EscapeWithFilterMarker (string txt)
 			int i = txt.IndexOf (filter, StringComparison.CurrentCultureIgnoreCase);
 			while (i != -1) {
 				sb.Append (GLib.Markup.EscapeText (txt.Substring (last, i - last)));
-				sb.Append ("<span color='blue'>").Append (txt.Substring (i, filter.Length)).Append ("</span>");
+				sb.Append ("<span color='blue'>").Append (txt, i, filter.Length).Append ("</span>");
 				last = i + filter.Length;
 				i = txt.IndexOf (filter, last, StringComparison.CurrentCultureIgnoreCase);
 			}

Mono.Addins.Setup/Mono.Addins.Setup.ProgressMonitoring/ProgressStatusMonitor.cs

@@ -102,7 +102,7 @@ void WriteLog (string text)
 				pi = i + 1;
 				i = text.IndexOf ('\n', pi);
 			}
-			logBuffer.Append (text.Substring (pi));
+			logBuffer.Append (text, pi, text.Length - pi);
 		}
 
 		public TextWriter Log {

Mono.Addins.Setup/Mono.Addins.Setup/PcFileCache.cs

@@ -546,7 +546,7 @@ string Evaluate (string value)
 			StringBuilder sb = new StringBuilder ();
 			int last = 0;
 			while (i != -1 && i < value.Length) {
-				sb.Append (value.Substring (last, i - last));
+				sb.Append (value, last, i - last);
 				if (i == 0 || value [i - 1] != '$') {
 					// Evaluate if var is not escaped
 					i += 2;
@@ -572,7 +572,7 @@ string Evaluate (string value)
 				if (i < value.Length - 1)
 					i = value.IndexOf ("${", i);
 			}
-			sb.Append (value.Substring (last, value.Length - last));
+			sb.Append (value, last, value.Length - last);
 			return sb.ToString ();
 		}
 	}

Mono.Addins.Setup/Mono.Addins.Setup/TextFormatter.cs

@@ -201,7 +201,7 @@ public void Append (string text)
 				}
 
 				if (n != sn)
-					currentWord.Append (text.Substring (sn, n - sn));
+					currentWord.Append (text, sn, n - sn);
 				if (foundSpace) {
 					AppendCurrentWord (text[n]);
 					n++;

Mono.Addins/Mono.Addins.Description/AddinDescription.cs

@@ -1009,7 +1009,8 @@ internal string ParseString (string input)
 			if (i == -1)
 				return input;
 
-			StringBuilder result = new StringBuilder (input.Substring (0, i), input.Length);
+			StringBuilder result = new StringBuilder (input.Length);
+			result.Append (input, 0, i);
 
 			while (i < input.Length) {
 				if (input [i] == '$') {