This module tries to keep pending stream management sessions of push
clients alive (as long as the disconnected clients are reachable via
push notifications).
The changes are very similar to those from previous commit:
* Now there is no need to pass validating function in
gen_mod:get_opt() and gen_mod:get_module_opt() functions,
because the modules' configuration keeps already validated values.
* New functions gen_mod:get_opt/2 and gen_mod:get_module_opt/3 are
introduced.
* Functions gen_mod:get_opt/4 and get_module_opt/5 are deprecated.
If the functions are still called, the "function" argument is
simply ignored.
* Validating callback Mod:listen_opt_type/1 is introduced to validate
listening options at startup.
If a pending stream management session times out, call
ejabberd_c2s:process_terminated/2 *before* storing the incoming stanza
count. Without this change, the session table entry that holds the
stanza count was purged while closing the session.
It's now possible to use files as internal packet queues.
The following options are introduced:
* queue_type: the option can be set to `ram` (default) or `file`.
The option can be set per virtual host.
* queue_dir: path to the directory where queues will be allocated.
The default is 'queue' directory inside Mnesia directory.
This is a global option and cannot be set per virtual host.
