Minimal fix for Calendar.setTimeZone.
The interpretation of Calendar's competing member variables when the time,
time zone, and fields[] don't agree is confusing, and led to
Calendar.setTimeZone having no effect. I've improved the documentation
based on my reverse-engineering and fixed this bug. I noticed a lot of
other code that looks incorrect though, and I've raised http://b/
2419810
suggesting that we switch to icu4j's calendars in the longer term.
Bug: http://code.google.com/p/android/issues/detail?id=6184