Comment 1 for bug 1189775

First Mir patch. :)

I added a method set_hotspot to Cursor, and an implementation in GBMCursor.

I made the hotspot a "geometry::Point" because someone using the interface will see the hotspot as a point on the cursor, but represent it internally as a "geometry::Displacement" to make the implementation easier.

I did some manual testing in the mir_demo_client_fingerprint app and it works :). I'll need to dig into the automated testing code so I can make some automatic tests for it.