repmgr standby switchover: add sanity check for pg_rewind useability

pg_rewind will only be executed on a demoted primary if explictly
requested, to prevent transactions on the primary, which
were never replicated, from being automatically overwritten.

If --force-rewind is provided, we'll need to check pg_rewind
is actually useable before we need to use it.

strutil.c

@@ -8,8 +8,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-
-
 #include "log.h"
 #include "strutil.h"