- add a new knob, WITH_SQL_REMOVE_DELETED, for explicitly activating
the new code for removing entries from the SQL log file when a user or
domain is deleted;
- add real NOPORTDOCS support and install the README.* files in addition
to the doc_html/ and man_html/ directories if NOPORTDOCS is not set;
- fix a couple of spelling and grammar errors in the new README.vpopmaild;
- add several sanity checks;
- remove the last traces of the ActiveDirectory backend;
- various other minor changes.
