Move configuration and installation questions and error messages
into separate files for easier customization and translation.
Fix typo noted by Brock Rozen.
Include recent additions.
Add leading blank line.
Move configuration questions into message files.
Increase the version number to 12.
Move installation messages into message files.
Allow customized "welcome" files to be displayed using the "doc" CGI
parameter.

For example, the CGI parameters func=welcome&doc=foo would cause the
"welcome_foo" file to be displayed.  The stock welcome file will be
displayed if the requested file is not found.
(set)  Return an error message if a setting is nonexistent
or used out of scope.  Thanks to Mohamed Lrhazi.
(ask_clear, ask_continue, ask_lang)
Add functions which prompt for screen clearing, pressing enter to
continue, and message language.

Move questions into message files.

Add the framework for future mysql backend support.
Move questions into message files.
(chownmod)  Separate failure cases and treat errors individually.
Add Exim 4 support.
Move messages into message files.
Move questions into message files.
Allow the parameters of an existing domain to be changed.
(get_addr)  Request and validate an e-mail address.

(get_enum)  Allow unambiguous, case-insensitive abbreviations
  of enumerated values (e.g., "i" for "ignore").

Move error messages into message files.

(get_passwd)  Request and validate a password, which must not contain
  internal spaces or tabs.

(retr_msg)  Return the contents of a message file.
Move messages into message files.
Minor rewording.
Correct typo.
Fix typos.  Thanks to Brock Rozen.
Add blank line.
Improve error checking.