mod_ssl: change behaviour of 'is_secure' setting; redirect to https when not specified otherwise.

(cherry picked from commit 6637c92478f5de1dc61683e7c03eaf0656024e1a)
mod_ssl: added an 'is_ssl' configuration to force a site to be served over ssl. Use in combination with 'is_secure'.

(cherry picked from commit 6b8e994043de59f8b24a159219574f0113ae9b9c)