flux_msg_handler_create(3): add get_handle_watcher

Problem: flux_get_handle_watcher() is not documented.

Add it to the message handler man page.

doc/Makefile.am

@@ -220,6 +220,7 @@ MAN3_FILES_SECONDARY = \
 	man3/flux_msg_handler_destroy.3 \
 	man3/flux_msg_handler_start.3 \
 	man3/flux_msg_handler_stop.3 \
+	man3/flux_get_handle_watcher.3 \
 	man3/flux_msg_handler_delvec.3 \
 	man3/flux_child_watcher_get_rpid.3 \
 	man3/flux_child_watcher_get_rstatus.3 \

doc/man3/flux_msg_handler_create.rst

@@ -28,6 +28,8 @@ SYNOPSIS
 
    void flux_msg_handler_stop (flux_msg_handler_t *mh);
 
+   flux_watcher_t *flux_get_handle_watcher(flux_t *h)
+
 Link with :command:`-lflux-core`.
 
 DESCRIPTION
@@ -46,7 +48,8 @@ The handle :var:`h` is monitored for FLUX_POLLIN events on the
 :type:`flux_reactor_t` associated with the handle as described in
 :man3:`flux_set_reactor`.  This internal "handle watcher" is started when the
 first message handler is started, and stopped when the last message handler
-is stopped.
+is stopped.  The handle watcher may be directly accessed with
+:func:`flux_get_handle_watcher`.
 
 Messages arriving on :var:`h` are internally read and dispatched to matching
 message handlers. If multiple handlers match the message, the following

doc/manpages.py

@@ -189,6 +189,7 @@
     ('man3/flux_msg_handler_create', 'flux_msg_handler_start', 'manage message handlers', [author], 3),
     ('man3/flux_msg_handler_create', 'flux_msg_handler_stop', 'manage message handlers', [author], 3),
     ('man3/flux_msg_handler_create', 'flux_msg_handler_create', 'manage message handlers', [author], 3),
+    ('man3/flux_msg_handler_create', 'flux_get_handle_watcher', 'manage message handlers', [author], 3),
     ('man3/flux_open', 'flux_clone', 'open/close connection to Flux Message Broker', [author], 3),
     ('man3/flux_open', 'flux_close', 'open/close connection to Flux Message Broker', [author], 3),
     ('man3/flux_open', 'flux_open', 'open/close connection to Flux Message Broker', [author], 3),