SunController.subsolarPoint() method is flawed

[Bruce Schubert]

• The internal JulianDate calculation is off by 30 and a fraction days (I suspect the Calendar.MONTH usage assumes 1 for January when in fact it is 0).
• The adjustment for greenwhichMeanSidereal throws things off.

See discussion here: https://groups.google.com/forum/#!topic/terramenta-dev/8SyVV3ESfHE

[Bruce Schubert]

Globe: Fixed SunlightController subsolarPoint calculation. Resolves #56. - Added a JRE6/7 Julian date method. Replaced subsolar point algorithm's internal JD computation with new JD method; changed computation of greenwich mean sidereal time.

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