do not autorelease build ids when a child of mysql-test-run.pl dies

# Requested IDs are stored in a hash and released upon END.

#

my %mtr_unique_assigned_ids = ();

my $mtr_unique_pid;

BEGIN {

	$mtr_unique_pid = $$ unless defined $mtr_unique_pid;

}

END { 

	if($mtr_unique_pid == $$) {

		while(my ($id,$file) = each(%mtr_unique_assigned_ids)) {

			print "Autoreleasing $file:$id\n";

			mtr_release_unique_id($file, $id);

		}

	}

}

#

# Require a unique, numerical ID, given a file name (where all