Fix 9.1 config parsing: wal_buffers configuration

[schmiddy]

If you try to parse a 9.1 config file, you will blow up like this:

Traceback (most recent call last):
  File "./pgtune", line 698, in <module>
    sys.exit(main(sys.argv))
  File "./pgtune", line 687, in main
    wizard_tune(config, options, settings)
  File "./pgtune", line 593, in wizard_tune
    if settings.memory_unit(key):
  File "./pgtune", line 402, in memory_unit
    return (self.param_to_dict[setting])['memory_unit']
KeyError: 'wal_buffers'

Since the pg_settings-9.1-64 file was missing a line about wal_buffers. Add that missing line, and solve the TODO noted about not needing to figure out wal_buffers at all. Now, the output postgresql.conf should just leave wal_buffers as it was, i.e. left at the auto-configured -1 by default.

[scottcc]

👍

[andreif]

Reference http://www.postgresql.org/docs/9.1/static/runtime-config-wal.html#GUC-WAL-BUFFERS