cron: Set the From-address to be the technical contact email address.

To avoid sending email with a From-address belonging to an external
domain, set it to the same as the technical contact address.

Thanks to Dick Visser for adding this!

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3021 44740490-163a-0410-bde0-09ae8108e29a