* Mother of all commits:

* Cleaned up copyright notices in AssemblyInfo.cs's
* Added Copyright headers to a bunch of files missing them
* Replaced several common string instances with a static constant to prevent reallocation of the same strings thousands of times. "" -> String.Empty is the first such candidate.

OpenSim/Framework/Util.cs

@@ -356,7 +356,7 @@ namespace OpenSim.Framework
             {
                 return capsURLS[userID];
             }
-            return "";
+            return String.Empty;
         }
 
         public static void SetCapsURL(LLUUID userID, string url)