Replace Tkinter code with pyQt code in fpdb_prerun.py

[astephane]

Replace Tkinter code with pyQt code in fpdb_prerun.py in order to remove Tkinter dependency.

[philroberts]

I think the point of fpdb_prerun is to check that dependencies are installed. Dependencies like pyQt. (of course, it is not safe to assume the tkinter works, either, but I didn't write this stuff.)

[astephane]

Sure, it's like a booststrap mechanism: no Qt UI packages are present, another Tk UI package is used to display in a window (usefull on Windows not so on Linux because we could simply trace to the console).

A better way to remove Tkinter could be to trace to the error log file and/or simply let Python module exception be raised and stop execution.

In deed, I installed Tkinter and I think this issue is not urgent.