[android] Support for time zones in Android.

The time zone database in Android sits in a non-standard place, and it
can be overridedn by a second location. Besides not sitting in a standard
place, it differs from other Unixes in that the database is bundled into
one binary file, and there are no folders with small files for each time
zone. Luckily the database is generated from Olson, so most of the
CFTimeZone code already handles the details.

The code implements a generic enumeration of the time zones contained in
the database (checking for both the override and the standard location).
The enumeration code is used for both enumerating the known time zones,
as well as creating time zones by name.

At many points there was code blocking the usage of time zones in
Android that has been removed.

This allows the tests in TestDateFormatter, TestCalendar and
TestTimeZone to pass on Android.

Author: drodriguez