the guest OS. The shortcut can be defined in the bochsrc or in the config
interface. It is possible to change it at runtime.
These shortcuts are currently recognized:
ctrlaltdel, ctrlaltesc, ctrlaltf1, alttab
Here is the list of changes:
* userbutton.h and userbutton.xpm added in gui/bitmaps
* config options for the userbutton shortcut added
* initialize the new button in the gui.cc
* the new userbutton handler generates keypresses and relaeses depending on
the shortcut keyword
* the gui stops adding buttons to the headerbar if not enough space is left.
This can happen when the screen width is 320 pixels (done for X11 only).
* TODO: build a dialog box for the wxWindows gui
