Bug 30517

sysinstall in Noninteractive mode only deletes existing partitions
if "partition" is set to "all" or "exclusive".  Sysinstall currently 
has no way to delete existing partitions from the drive. 
We are working on reimaging a number of systems through automated 
installs, and we need to have multiple slices due to the 8 partitions 
per slice limit (yeah I'd prefer to fix that to, but...).  Anyway this 
requires us to specify the initial partition(s) size, and then use 
"free" for the last one.

This small patch allows you to have an install.cfg file that looks like
this:

---snip---
disk=da0 
# ~5 Gigs  
deletedisk=YES
partition=10340000
# partition=all
bootManager=standard   
diskPartitionEditor

disk=da0
partition=free
bootManager=standard 
diskPartitionEditor
---snip---

So that all existing partitions get deleted on the first call to
diskPartitionEditor.

Fix: 

Apply the following (small) context diff.  I realize that investing
more energy in sysinstall is probably wasted, but this is a very
minimal patch, and doesn't affect any existing functionality, so its
probably worth it.

 http://www.pcslink.com/~ryan/sysinstall.patch