pg_combinebackup: Add --version to --help output

(It was already on the man page.)

src/bin/pg_combinebackup/pg_combinebackup.c

@@ -738,6 +738,7 @@ help(const char *progname)
 			 "                            use algorithm for manifest checksums\n"));
 	printf(_("      --no-manifest         suppress generation of backup manifest\n"));
 	printf(_("      --sync-method=METHOD  set method for syncing files to disk\n"));
+	printf(_("  -V, --version             output version information, then exit\n"));
 	printf(_("  -?, --help                show this help, then exit\n"));
 
 	printf(_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);