briannesbitt/Carbon — pull request #5 by flevour (2012-10-11 19:04:43+00:00)
Title: Implement __isset

I turns out that some systems out there (for example Twig) require an object to implement __isset whenever it uses __get. In this way they can test whether a given method/property exist before referencing it.
I encountered such an issue when trying to use Carbon inside a Twig template (see more here http://twig.sensiolabs.org/doc/recipes.html#using-dynamic-object-properties).

This PR introduces the __isset method and the appropriate tests.