dropHandler: Global filename access about mpkedit

[bryc]

Now that everything is contained within an anonymous function, there's no reason not to use a global variable - $MPK is already a global, anyway. So I simply set a global during readData, and other functions will read this.

[bryc]

Filename is now part of the State object as used as the currently open file state

[bryc]

The parser module has a global variable for the current file, for debugging purposes. Not elegant but works, for now. Still better than passing filename as an argument to each function simply for debugging purposes.