Output which logs dir doesn't exist in error message.
Fix link to wiki page.
Do not hard code some random PHP version in X-Mailer.

It just doesn't make any sense and can only cause confusion.
Add the changemanipulation permission to the dist config.

Defaults to true.
Add required encryption.enable setting to dist config.
Various documentation tweaks.

Typos and clarifications discovered while installing janus.
Merge pull request #501 from thijskh/develop

Various tweaks and documentation improvements