Editing tools for AIX-style stanza config files

Promises for dealing with stanza-based configuration files commonly
used on AIX systems.

The following are agent bundles for use in method calls:

 create_stanza(configfile, stanza)
    - Adds a new empty stanza to the specified config file.
 set_stanza_attrib(configfile, stanza, attribute, value)
    - Ensures that given stanza and attribute are present in the
      file, and that the attribute is set to the given value.
 remove_stanza_attrib(configfile, stanza, attribute)
    - Ensures that no attribute of the specified name exists in
      the given stanza in the config file.
 delete_stanza(configfile, stanza)
    - Ensures that no stanza of the specified name exists in the
      config file. Deletes the stanza and all its attributes
      if necessary.

The edit_line bundles can also be used directly if desired, by following
the example of the agent bundles.