Document the new visibility rules for bcc-recpt.
Clarify the documentation for mark-as-read.

everywhere.  Tighten the rules so that secret info cannot leak through
get-text-stat.  Re-indent text.c.  Add a few const qualifiers all over
the code.

get-session-info and who-is-on family of functions.  Test cases added.

Documented the allowed-content-type aux item.

users who are not members of the BCC recipient in question.

Re-read aux-item definition file on a WINCH signal.

Bug fix in validation regexp for mx-date
Reserved a range of aux-items for komimportmail

Miscellaneous documentation fixes.

files.  Fix.  Remove false warnings.

documentation of add-recipient, async-new-recipient and
async-sub-recipient.  Don't overwrite installations that have
lyskomd-backup but no lyskomd-data.

minor bug that currently had no effects.  Fixed a buffer overrun.
Code cleanup.