pg_dumpall: Include --verbose option in --help output

The -v/--verbose option was not included in the output from --help for
pg_dumpall even though it's in the pg_dumpall documentation and has
apparently been around since pg_dumpall was reimplemented in C in 2002.

Fix that by adding it.

Pointed out by Daniel Westermann.

Back-patch to all supported branches.

Discussion: https://www.postgresql.org/message-id/2020970042.4589542.1482482101585.JavaMail.zimbra%40dbi-services.com

src/bin/pg_dump/pg_dumpall.c

@@ -543,6 +543,7 @@ help(void)
 
 	printf(_("\nGeneral options:\n"));
 	printf(_("  -f, --file=FILENAME          output file name\n"));
+	printf(_("  -v, --verbose                verbose mode\n"));
 	printf(_("  -V, --version                output version information, then exit\n"));
 	printf(_("  --lock-wait-timeout=TIMEOUT  fail after waiting TIMEOUT for a table lock\n"));
 	printf(_("  -?, --help                   show this help, then exit\n"));