I copied over the rmtree function (and other functions needed by this one)

from the postgresql code so we use that instead of issuing system calls
with rm -rf ....

I also eliminated the rm -rf for pg_xlog.

Will later do the same with the other system call to remove files
in pg_replslot/

repmgr.h

@@ -28,6 +28,7 @@
 #include "dbutils.h"
 #include "errcode.h"
 #include "config.h"
+#include "dirmod.h"
 
 #define MIN_SUPPORTED_VERSION		"9.3"
 #define MIN_SUPPORTED_VERSION_NUM	90300