bogofilter: install postfix-bogofilter script

Signed-off-by: W. Michael Petullo <mike@flyn.org>
Merge remote-tracking branch 'openwrt/master' into bogofilter
bogofilter: depend on db47 with statistics support

Signed-off-by: W. Michael Petullo <mike@flyn.org>
bogofilter: create /usr/sbin before installing postfix-bogofilter there

Signed-off-by: W. Michael Petullo <mike@flyn.org>
Merge pull request #435 from MikePetullo/bogofilter

bogofilter: depend on db47 with statistics support