* Upgrades existing data so that the groupmembersonly option is
replaced with equivalent data for the new availability API.
* Removes the database field and admin setting used for
groupmembersonly.
* Changes core modinfo library to remove/deprecate groupmembersonly
data and functions.
* Changes other core library files to remove groupmembersonly
references.
Includes deprecation of several functions, listed in lib/upgrade.txt.
Changes core code to use new API instead of the old one when
checking user access to activities and sections.
Includes changes to other libraries that are necessary after
adding the availability system and removing old conditional tables
etc.
