Add support for non-Gregorian calendars
When using a calendar that is not the Gregorian calendar (in my case, I use the Japanese one, but I'm willing to bet it also happens with other calendars like the Hebrew one), many date-based operations in the PlasticSCM client break, including but not limited to:
- Branch Explorer
- Changesets (the action in the left menu, below Branch Explorer)
This means that at this moment, I am unable to use said features without changing my OS' calendar back to the Gregorian one.