postfix: added default values for postfix_use_... amavisd, dovecot, schleuder, and sympa configuration variables (default to "no").

This is needed to make the changes introduced by the merge from sarava/master backward compatible.

An "invalid tag" error was thrown is the value was something like "[10.1.2.3]".
The trick was to surround the value with single quotes.
Thanks gmambro for the bug report.

Based on a suggestion and patch from Nick Anderson. Thanks !

find . -type f -exec perl -pi -e 's/postfix-ng/postfix/' {} \;