Add the ability to specify option extra cost items for event registrations.

This functionality should be covered by the "Price Sets" contribution that is being devloped by Marshall Newrock, which is scheduled to be incorporated into CiviCRM core for the 1.8 release.

The specifications are here:
http://wiki.civicrm.org/confluence/display/CRM/Price+Sets
(dgg)

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For example:

Event is free, but one may chose to add any of these items:

Mug: $10
Lunch: $20
Jacket: $50
Paper Proceedings: $35

While one could create several different membership levels, it would quickly get cumbersome if there are more than 2 optional items that may be picked separately.