Merge pull request ruby-ldap#46 from epeli/patch-1

Add result string 19 Constraint Violation

Author: Rory O'Connell

lib/net/ldap.rb

@@ -323,6 +323,7 @@ class LdapError < StandardError; end
     14 => "saslBindInProgress",
     16 => "No Such Attribute",
     17 => "Undefined Attribute Type",
+    19 => "Constraint Violation",
     20 => "Attribute or Value Exists",
     32 => "No Such Object",
     34 => "Invalid DN Syntax",