Not all "end" events have to be considered bogus connections

Instead, consider receiving a premature stream end while a query
is in progress as an error sign, bubbling up the error to the
client level. Fixes the testsuite while still fixing my cases
and possibly brianc#458.

The correct fix would be to provide a .validate method to the
pooler, and expose a .validate method to the client and to the
connection classes for that purpose...

lib/client.js

@@ -177,6 +177,7 @@ Client.prototype.connect = function(callback) {
       var disconnectError = new Error('Stream unexpectedly ended during query execution');
       self.activeQuery.handleError(disconnectError);
       self.activeQuery = null;
+      self.emit('error', disconnectError);
     }
     self.emit('end');
   });

lib/pool.js

@@ -33,11 +33,6 @@ var pools = {
             pool.destroy(client);
           });
 
-          // Remove client from pool on connection end
-          client.on('end', function() {
-            pool.destroy(client);
-          });
-
           return cb(null, client);
         });
       },