Add functionality to "pause" repmgrd

In some circumstances, e.g. while performing a switchover, it is essential
that repmgrd does not take any kind of failover action, as this will put
the cluster into an incorrect state.

Previously it was necessary to stop repmgrd on all nodes (or at least
those nodes which repmgrd would consider as promotion candidates), however
this is a cumbersome and potentially risk-prone operation, particularly if the
replication cluster contains more than a couple of servers.

To prevent this issue from occurring, this patch introduces the ability
to "pause" repmgrd on all nodes wth a single command ("repmgr daemon pause")
which notifies repmgrd not to take any failover action until the node
is "unpaused" ("repmgr daemon unpause").

"repmgr daemon status" provides an overview of each node and whether repmgrd
is running, and if so whether it is paused.

"repmgr standby switchover" has been modified to automatically pause repmgrd
while carrying out the switchover.

See documentation for further details.

repmgr-client-global.h

@@ -97,6 +97,7 @@ typedef struct
 	bool		force_rewind_used;
 	char		force_rewind_path[MAXPGPATH];
 	bool		siblings_follow;
+	bool		repmgrd_no_pause;
 
 	/* "node status" options */
 	bool		is_shutdown_cleanly;
@@ -156,7 +157,7 @@ typedef struct
 		/* "standby register" options */ \
 		false, -1, DEFAULT_WAIT_START,   \
 		/* "standby switchover" options */ \
-		false, false, "", false,		   \
+		false, false, "", false, false,	\
 		/* "node status" options */ \
 		false, \
 		/* "node check" options */ \
@@ -193,6 +194,14 @@ typedef enum
 } t_server_action;
 
 
+typedef struct ColHeader
+{
+	char		title[MAXLEN];
+	int			max_length;
+	int			cur_length;
+} ColHeader;
+
+
 
 /* global configuration structures */
 extern t_runtime_options runtime_options;
@@ -228,7 +237,10 @@ extern void get_superuser_connection(PGconn **conn, PGconn **superuser_conn, PGc
 extern bool remote_command(const char *host, const char *user, const char *command, PQExpBufferData *outputbuf);
 
 extern void make_remote_repmgr_path(PQExpBufferData *outputbuf, t_node_info *remote_node_record);
+
+/* display functions */
 extern void print_help_header(void);
+extern void print_status_header(int cols, ColHeader *headers);
 
 /* server control functions */
 extern void get_server_action(t_server_action action, char *script, char *data_dir);