[threeten-dev] Review updates to support multiple Hijrah deviations

[Roger Riggs]

Hi,

This review addresses some of the issues in #95 Deviation Options for 
the Hijrah Calendar <https://github.com/ThreeTen/threeten/issues/95>

Please review and comment on: 
http://cr.openjdk.java.net/~rriggs/webrev-deviations/

The changes include refactoring the support for the deviations into the 
Chrono class
from the HijrahDate class.  The change includes changing HijrahDate so 
that it refers
explicitly to an instance of HijrahChrono.  Changes to HijrahChrono 
include multiple
instances with different Ids and calendarTypes that encapsulate the 
different deviations.
Each acts as a different calendar.  The serialized form of HijrahDate 
includes the reference
to the HijrahChrono instance (already serialized as represented by the id).

The format of the deviation file is modified to use ISO dates which are 
converted to
HijrahDates using the default Islamic calendar.  The offsets modify the 
length of the
HijrahMonths for the alternate calendar.

The configuration mechanism for the deviation options is not final.  
System properties
identify the additional Hijrah calendars; and the default location of 
the deviation files
which are named according to the calendar id.
The additional calendars are created when the standard Hijrah calendar 
is initialized.

These changes also exposed a flaw in the registration mechanism used for 
Chrono.of(id);
the registration was being done before the constructor of the Chrono was 
complete
allowing incompletely constructed Chronos to be visible to other threads.
A separate registerChrono method was added that is the last thing called in
the subclasses constructor.

There may be a better initialization sequence but it cannot involve 
recursion between
the static initializers and the constructors.

Happy Holidays, Roger