This is 33rd iteration of typo fixes

CLI 'add server' handler relies on usermsgs_ctx to display errors in
internal function on CLI output. This may be also extended to other
handlers.

However, to not clutter stderr from another contextes, usermsgs_ctx must
be resetted when it is not needed anymore. This operation cannot be
conducted in the CLI parse handler as display is conducted after it.

To achieve this, define new CLI states CLI_ST_PRINT_UMSG /
CLI_ST_PRINT_UMSGERR. Their principles is nearly identical to states for
dynamic messages printing.

Rename CLI_ST_PRINT_FREE to CLI_ST_PRINT_DYNERR.

Most notably, this highlights that this is reserved to error printing.

This is done to ensure consistency between CLI_ST_PRINT/CLI_ST_PRINT_DYN
and CLI_ST_PRINT_ERR/CLI_ST_PRINT_DYNERR. The name is also consistent
with the function cli_dynerr() which activates it.

Stores the mcli_reload bind_conf in order to identify it later.

mworker_cli_proxy_new_listener() now returns a bind_conf * or NULL upon
failure.

Now that the CLI's print context is alone in the appctx, it's possible
to refine the appctx's ctx layout so that the cli part matches exactly
a regular svcctx, and as such move the CLI context into an svcctx like
other applets. External code will still build and work because the
struct cli perfectly maps onto the struct cli_print_ctx that's located
into svc.storage. This is of course only to make a smooth transition
during 2.6 and will disappear immediately after.

A tiny change had to be applied to the opentracing addon which performs
direct accesses to the CLI's err pointer in its own print function. The
rest uses the standard cli_print_* which were the only ones that needed
a small change.

The whole "ctx.cli" struct could be tagged as deprecated so that any
possibly existing external code that relies on it will get build
warnings, and the comments in the struct are pretty clear about the
way to fix it, and the lack of future of this old API.

New function cli_list_keywords() scans the list of registered CLI keywords
and dumps them on stdout. It's now called from dump_registered_keywords()
for the class "cli".

Some keywords are valid for the master, they'll be suffixed with
"[MASTER]". Others are valid for the worker, they'll have "[WORKER]".
Those accessible only in expert mode will show "[EXPERT]" and the
experimental ones will show "[EXPERIM]".

"f(void)" is the correct and preferred form for a function taking no
argument, while some places use the older "f()". These were reported
by clang's -Wmissing-prototypes, for example:

  src/cpuset.c:111:5: warning: no previous prototype for function 'ha_cpuset_size' [-Wmissing-prototypes]
  int ha_cpuset_size()
  include/haproxy/cpuset.h:42:5: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
  int ha_cpuset_size();
      ^
                     void

This aggregate patch fixes this for the following functions:

   ha_backtrace_to_stderr(), ha_cpuset_size(), ha_panic(), ha_random64(),
   ha_thread_dump_all_to_trash(), get_exec_path(), check_config_validity(),
   mworker_child_nb(), mworker_cli_proxy_(create|stop)(),
   mworker_cleantasks(), mworker_cleanlisteners(), mworker_ext_launch_all(),
   mworker_reload(), mworker_(env|proc_list)_to_(proc_list|env)(),
   mworker_(un|)block_signals(), proxy_adjust_all_maxconn(),
   proxy_destroy_all_defaults(), get_tainted(),
   pool_total_(allocated|used)(), thread_isolate(_full|)(),
   thread(_sync|)_release(), thread_harmless_till_end(),
   thread_cpu_mask_forced(), dequeue_all_listeners(), next_timer_expiry(),
   wake_expired_tasks(), process_runnable_tasks(), init_acl(),
   init_buffer(), (de|)init_log_buffers(), (de|)init_pollers(),
   fork_poller(), pool_destroy_all(), pool_evict_from_local_caches(),
   pool_total_failures(), dump_pools_to_trash(), cfg_run_diagnostics(),
   tv_init_(process|thread)_date(), __signal_process_queue(),
   deinit_signals(), haproxy_unblock_signals()

Only mworker uses proc_self, and it was declared in global.h, forcing
users of global.h to include mworker and its dependencies.

Moving it to mworker reduces the preprocessed size of version.c from
170 to 125kB by shrinking the number of local includes from 30 to 16
and the number of system includes from 147 to 132.

This function will be useful to check if the keyword is already registered.
Also add a define for the max number of args.

This will be needed by a next patch to fix a bug and will have to be
backported.