default dateFormat better to be 'dd/mm/yy'

currently the default dateFormat(when nothing is specified) is set to 'mm/dd/yy'. This make support of i18n more complicated than expected. A typical situation is 'en-CA' which when use short datetime is 'dd/mm/yy' yet the i18n package doesn't have it.

I use conditional include of specific javascript file per page(and only load in the correct i18n datepicker supplement function as needed). In this case, en-CA failed(but silently). As a result, when the data is shown and passed back, it can be a problem for things like '11/12/2012' but siliently passed most checking.

The simplest solution is of course create 'en-CA.js' but from a grand scale, there can be many different language that may not be included in the i18n package and all would fail in similar ways.

If the default is set to 'dd/mm/yy'(so basically en-UK), at least it would work as US is the only country that use 'mm/dd/yy' and it is quite easy to just make sure 'en-US.js' is there and would be loaded if needed.