easygui multchoicebox does not work on Win7, python 2.7.9

[jurop88]

as per subject. The choicebox is always in 'single selection' mode.
The problem lies in the scope of the global variable __choiceboxMultipleSelect. A simple modification in the lines 472-473 and 493-494 (remove global, add bb. in front of the variable) in the file derived_boxes.py does the trick for me.
New to GitHub, so sorry if this could have been done easily in other ways.

[robertlugg]

Thanks for the report. Should be fixed with #69. Change went into 'master'. 'develop' did not have the issue.