* #19501: Only the first user of multi-user IPO's were getting converted to AnimData.
Now, this AnimData gets converted multiple times - once for each user. This will mean that multi-user actions will no longer be multi-user after conversion though, although this could be fixed manually if there really is such a need.
* #19503: Nasty memory leaks when duplicating objects with AnimData
Fixed a few little oversights made when coding the copying code for NLA-data (which resulted in exponential copying-loops of doom), and sanitised the AnimData copying code for ID-blocks to be simpler to manage.