Add configuration parameter "repmgr_bindir"

This is to facilitate remote invocation of repmgr when the repmgr
binary is located somewhere other than the PostgreSQL binary directory, as it
cannot be assumed all package maintainers will install repmgr there.

This parameter is optional; if not set (the default), repmgr will fall back
to "pg_bindir" (if set).

Addresses GitHub #246.

repmgr-action-cluster.c

@@ -999,7 +999,7 @@ build_cluster_matrix(t_node_matrix_rec ***matrix_rec_dest, int *name_length)
 		 */
 		appendPQExpBuffer(&command,
 						  "\"%s -d '%s' ",
-						  make_pg_path(progname()),
+						  make_repmgr_path(progname()),
 						  cell->node_info->conninfo);
 
 
@@ -1182,7 +1182,7 @@ build_cluster_crosscheck(t_node_status_cube ***dest_cube, int *name_length)
 
 		appendPQExpBuffer(&command,
 						  "%s -d '%s' --node-id=%i ",
-						  make_pg_path(progname()),
+						  make_repmgr_path(progname()),
 						  cell->node_info->conninfo,
 						  remote_node_id);