change ad_verify_and_get_user_id to ad_conn user_id, change ad_maybe_redirect_for_registration to auth::require_login, make some db_ and dt_ function -public
1. Added a new Tcl procedure to the content repository's library, named cr_write_content, which properly writes content to the connection regardless of RDBMS and storage type. This simplified a bunch of stuff (which explains the removed files).
2. Fixed a lot of general comments issues regarding HTML vs. Plain/Text, attachments, etc.