Streaming replication document improvements

Hi,

The attached patch improves the documents about SR as follows:

* Improve the description about the setup procedure of SR.
  o Add the link to the recovery.conf parameter if needed.
  o Add the example of recovery.conf setting.
* Document what should be monitored for avoiding the disk full
  failure on the primary.
* Clarify how to safely take an incrementally updated backups.
* Define the recovery.conf parameters as an index term.
* Describe how to use recovery.conf.

Any comments are welcome.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center