Initial implementation of "repmgr master unregister"

Also adds "--dry-run" option

repmgr-client-global.h

@@ -23,6 +23,7 @@ typedef struct
 
 	/* general configuration options */
 	char		config_file[MAXPGPATH];
+	bool		dry_run;
 	bool		force;
 	char		pg_bindir[MAXLEN]; /* overrides setting in repmgr.conf */
 
@@ -75,7 +76,7 @@ typedef struct
 		/* configuration metadata */ \
 		false, false, false, false,	false, 	\
 		/* general configuration options */	\
-		"", false, "", \
+		"", false, false, "",			\
 		/* logging options */ \
 		"", false, false, false, \
 		/* database connection options */ \