Major changes for reading/parsing/validating configuration files.

Major changes for reading/parsing/validating configuration files.

* Split validator into 2 parts:
  - basicvalidator, for the core part,
  - confparser, mail.filter specific part.
* Split parser into 2 parts:
  - basicparser, for the core part,
  - confparser, mail.filter specific part.
* confparser now cache parser result for faster processing.
* And some minor changes and bugfixes.
git-archimport-id: frederic@jolliton.com--2004-private/mail-filter--main--0.1--patch-2