Give installs an installation key which we send back to mahara.org to prevent people sending bogus data for other peoples' wwwroots.

These constraints won't work on MySQL. Tough.

Converting to a bigint is way overkill, but I'mna blame XMLDB for that.

Conflicts:

	htdocs/lib/version.php

(cherry picked from commit 4bb025de)

Conflicts:

	htdocs/lib/version.php

copied by everyone.

Triggered, guess when - when a use joins a group!

The UI for this still needs to be implemented.

This also adds a database column to store the setting.

Whether this setting is even settable is controled by the site setting added in the previous commit.

Changes to each group file to make them visible to the public are coming in the next commit.

The process of copying profile views takes ages. Furthermore, the View
class appears to have some memory leaks that mean the upgrade soon runs
out of memory (tested on a ~2000 user site, the 64M limit is reached
reasonably soon).

After this, the upgrade finishes in a few seconds, rather than waiting
over a minute before dying (on test site).

There is a configuration parameter that sets how often this field is updated. This prevents DB writes every page load, though this behaviour can be achieved by setting the parameter to 0 if necessary.

Haven't tested SSO updating it yet.

- can_view_view needs http://paste.dollyfish.net.nz/0e6800 (see comment
  in function)
- blocktype/mygroups/lib.php is BROKEN (was using get_associated_groups
  which I guess has been removed. needs updating! I commented out a line
  to stop it fataling in the meantime.

Up the length of the username column to 100 characters, so it fits in "deleted" information on top of the 30 character limit enforced at the application level.
(cherry picked from commit e2319031)