Reroute errback to deferred returned by search()

The LDAPEntryWithClient.search() method used to send the LDAP request with
a call like
	self.client.send_multiResponse(... )
send_multiResponse() returns a deferred that was just discarded. If the
operation causes an error then the errback fired on the discarded deferred
will remain unhandled. The deferred returned by search() will then not
have any errback fired and the caller of search() will be waiting forever.

This change adds an errback to the deferred returned by send_multiResponse()
and has the error rerouted to the errback chain of the deferred returned by
search().

ldaptor/protocols/ldap/ldapsyntax.py

@@ -683,7 +683,7 @@ def search(self,
                 typesOnly=typesOnly,
                 filter=filterObject,
                 attributes=attributes)
-            self.client.send_multiResponse(
+            dsend = self.client.send_multiResponse(
                 op, self._cbSearchMsg,
                 d, cb, complete=not attributes,
                 sizeLimitIsNonFatal=sizeLimitIsNonFatal)
@@ -692,6 +692,11 @@ def search(self,
         else:
             if callback is None:
                 d.addCallback(lambda dummy: results)
+            def rerouteerr(e):
+                d.errback(e)
+                # returning None will stop the error
+                # from being propagated and logged.
+            dsend.addErrback(rerouteerr)
         return d
 
     def lookup(self, dn):