ctdb: Adding memory pool for queue callback

[Douglas Bagnall]

A very immaterial point:

On 8/11/18 5:28 AM, Swen Schillig via samba-technical wrote:
> 	t = clock();
> 	for (i = 0; i < 100000000; i++) {
                         ^^^^^^^^

> 	printf("It took %f seconds to execute 10 million talloc/free cycles.\n", tt);
                                              ^^^^^^^^^^

That is 100 million by my count.

Douglas