(ITS#6521) docs: pcache overlay section in admin guide

[jonathan@phillipoux.net]

Full_Name: Jonathan Clarke
Version: irrelevant
OS: irrelevant
URL: ftp://ftp.openldap.org/incoming/jcl-admin-guide-overlays-20100414.patch
Submission from: (NULL) (82.127.99.208)


The section of the admin guide on the proxy cache overlay is a little out of
date.

The patch below:
- updates deprected keywords to their new names (s/proxyAttrset/pcacheAttrset/,
etc)
- adds a configuration example for back-config, which is not trivial to guess