KPropertiesDialog: simplify button box usage, fix behavior on Esc
Review Request #128494 - Created July 21, 2016 and submitted
slotCancel() isn't called when pressing Esc or closing the window with the window manager button. Doing this the more standard way (reimplementing accept() and reject()) simplifies the code (since KPageDialog sets up the buttonbox this way already) and will be useful for knewfilemenutest which calls accept() on all types of dialog.
Looking at the output from kpropertiesdialogtest, to ensure the signals are emitted, and only once.
Tested OK, Cancel, Esc, Alt+F4.