allocating certain data structures.  (Bug 164).
* src/server/simple-cache.c (existing_confs): New static
variable.
(cached_no_of_existing_conferences): Return existing_confs,
instead of overestimating the number of conferences as
next_free_num.  (Bug 164).
(cached_create_conf): Increase existing_confs.
(cached_delete_conf): Decrease existing_confs.
(init_cache): Increase existing_confs when a new conference is
created.
(free_all_cache): Decrease existing_confs when conferences are
deallocated.
(dump_cache_mem_usage): Dump existing_confs.
* src/server/testsuite/config/unix.exp (check_memory_usage): Check
the dump of existing_confs.  Fail if allocated_strings or
allocated_blocks isn't found in the file.