BUG #4522: autovacuum working send SIGUSR1 to the wrong pid

The following bug has been logged online:

Bug reference:      4522
Logged by:          Zou Yong
Email address:      springwell@gmail.com
PostgreSQL version: 8.3.4
Operating system:   Linux 2.6.24
Description:        autovacuum working send SIGUSR1 to the wrong pid
Details:

I was running postgres on a Linux with busybox. The autovacuum feature is
turned on. I noticed that the autovacuum worker sent SIGUSR1 to pid 1 which
is the init process and caused the system halt.

I did some debugging and found that the root cause is the constant
AutoVacNumSignals is not defined correctly. It should be (AutoVacRebalance +
1).