UPDATE: Now when you set the Pokemon's held item, the Pokemon's form will change if appropriate. For instance, if you make Giratina hold the Griseous Orb, it will change to its Origin Forme. If you make it hold a different item, it will change to its Altered Forme. Same deal with Arceus and Genesect.
Also, if you change a Pokemon's form either manually or by changing its item, the Pokemon's ability will change to reflect the new form if necessary. Right now this applies to Shaymin, Giratina, Tornadus, Thundurus, Landorus, and Kyurem.
Great news for Mac users - Mac OS X is a go!
https://www.dropbox.com/sh/rms3mr0j2gisrgj/sYasuN7JED