* Edits to apply organizational improvements made in the HAWQ version, using consistent realm and domain names, and testing that procedures work.

* Convert tasks to topics to fix formatting. Clean up pg_ident.conf topic.

* Convert another task to topic

* Remove extraneous tag

* Formatting and minor edits

* - added $ or # prompts for all code blocks
- Reworked section "Mapping Kerberos Principals to Greenplum Database Roles" to describe, generally, a user's authentication process and to more clearly describe how principal name is mapped to gpdb name.

* - add krb_realm auth param

- add description of include_realm=1 for completeness