Update exceptions for File.Replace (#7290)

Author: gewarren

xml/System.IO/File.xml

@@ -4631,7 +4631,11 @@ The following example moves a file.
 
  -or-  
 
- The caller does not have the required permission.</exception>
+The caller does not have the required permission.
+
+-or
+
+<paramref name="sourceFileName" /> and <paramref name="destinationFileName" /> specify the same existing directory.</exception>
       </Docs>
     </Member>
     <Member MemberName="Replace">
@@ -4742,7 +4746,11 @@ The following example moves a file.
 
  -or-  
 
- The caller does not have the required permission.</exception>
+The caller does not have the required permission.
+
+-or
+
+<paramref name="sourceFileName" /> and <paramref name="destinationFileName" /> specify the same existing directory.</exception>
       </Docs>
     </Member>
     <Member MemberName="ResolveLinkTarget">