doc: document flux_watcher_set_priority(3)

Problem: There is no documentation for flux_watcher_set_priority(3).

Add it in the docs.

doc/Makefile.am

@@ -114,6 +114,7 @@ MAN3_FILES_PRIMARY = \
 	man3/flux_timer_watcher_create.3 \
 	man3/flux_periodic_watcher_create.3 \
 	man3/flux_idle_watcher_create.3 \
+	man3/flux_watcher_set_priority.3 \
 	man3/flux_msg_handler_create.3 \
 	man3/flux_msg_cmp.3 \
 	man3/flux_msg_create.3 \

doc/man3/flux_idle_watcher_create.rst

@@ -78,4 +78,4 @@ libev: http://software.schmorp.de/pkg/libev.html
 SEE ALSO
 ========
 
-:man3:`flux_watcher_start`, :man3:`flux_reactor_run`
+:man3:`flux_watcher_start`, :man3:`flux_reactor_run`, :man3:`flux_check_watcher_create`

doc/man3/flux_watcher_set_priority.rst

@@ -0,0 +1,42 @@
+===========================
+flux_idle_watcher_create(3)
+===========================
+
+.. default-domain:: c
+
+SYNOPSIS
+========
+
+.. code-block:: c
+
+   #include <flux/core.h>
+
+   flux_watcher_t *flux_watcher_set_priority (flux_watcher_t *w,
+                                              int priority);
+
+Link with :command:`-lflux-core`.
+
+DESCRIPTION
+===========
+
+:func:`flux_watcher_set_priority` sets the priority on the watcher.
+Higher priority watchers run first.  The range of priorities is from
+-2 to 2, with the default being 0.  If the priority is out
+of range, the max or min value is set.
+
+This function is a no-op if the underlying watcher does not support priorities.
+Currently only the check watcher supports priorities.
+
+
+RESOURCES
+=========
+
+.. include:: common/resources.rst
+
+libev: http://software.schmorp.de/pkg/libev.html
+
+
+SEE ALSO
+========
+
+:man3:`flux_check_watcher_create`

doc/manpages.py

@@ -286,6 +286,7 @@
     ('man3/flux_watcher_start', 'flux_watcher_destroy', 'start/stop/destroy/query reactor watcher', [author], 3),
     ('man3/flux_watcher_start', 'flux_watcher_next_wakeup', 'start/stop/destroy/query reactor watcher', [author], 3),
     ('man3/flux_watcher_start', 'flux_watcher_start', 'start/stop/destroy/query reactor watcher', [author], 3),
+    ('man3/flux_watcher_set_priority', 'flux_watcher_set_priority', 'set watcher priority', [author], 3),
     ('man3/hostlist_create', 'hostlist_create', 'Manipulate lists of hostnames', [author], 3),
     ('man3/hostlist_create', 'hostlist_destroy', 'Manipulate lists of hostnames', [author], 3),
     ('man3/hostlist_create', 'hostlist_decode', 'Manipulate lists of hostnames', [author], 3),