SabreDAV migrate script for version 3.2

This script help you migrate from a 3.1 database to 3.2 and later

Changes:
* Created a new calendarinstances table to support calendar sharing.
* Remove a lot of columns from calendars.

Keep in mind that ALTER TABLE commands will be executed. If you have a large
dataset this may mean that this process takes a while.

Make a back-up first. This script has been tested, but the amount of
potential variants are extremely high, so it's impossible to deal with every
possible situation.

In the worst case, you will lose all your data. This is not an overstatement.

Lastly, if you are upgrading from an older version than 3.1, make sure you run
the earlier migration script first. Migration scripts must be ran in order.

Usage:

php  [pdo-dsn] [username] [password]

For example:

php  "mysql:host=localhost;dbname=sabredav" root password
php  sqlite:data/sabredav.db