fix for defect #18233 Hebrew date of 13/23/5774, 12:00 AM flagged as
invalid. Case of 13 months in leap year.
Fix heading tests (fix TRAC ticket
https://bugs.dojotoolkit.org/ticket/18162)
Button DOH test: introduce tolerance threshold for size comparison to fix failures in latest FF, Chrome, and IE10 (and add missing semi-columns)
Refs #16806. Do not add mblBackground CSS class on the page if the config flag mblApplyPageStyles is set to false
Correct date returned by dojox.date.islamic.Date.toGregorian for a leap year. Fixes #18278.

If the Gregorian date being calculated is within the month before a leap year (for example Dec 1999 or Dec 2011) then the function dojox.date.islamic.Date.toGregorian returns a wrong value.
The issue is with the new Date constructor call and the calculation of the Gregorian leap year. Because the rest of the algorithm uses a 1-based month, the variable month is set to 12. But the Date constructor is 0-based and when new Date(1999, 12, 1) is called it returns Jan 1 2000 which turns out to be a leap year. This makes Gregorian date returned to be 1 less then actual it should be.
Correct wrong property name

Fixes #12630, #14944.
Do not touch nodes that do not exist

Fixes #18289.