#234 allow to disable hidden files in Unix/Linux

[Witek Mozga]

Tweaking the file tkfbox.tcl allows to make displaying hidden files in Linux/Unix optional by changing lines:
set ::tk::dialog::file::showHiddenVar 0
set ::tk::dialog::file::showHiddenBtn 1
It should be set like this for Linux/Unix by default. It would give much better experience to the user.

[Witek Mozga]

or maybe add an option to this dialog, something like -disable_hidden