src/xlib-util.lisp (with-xlib-protect): Limit X errors ignored to prevent freezes and add a backtrace system.

[PATCH] CLFSWM should depend on sb-posix since src/tools.lisp uses sb-posix:getenv & sb-posix:putenv.

src/clfswm-internal.lisp (clean-windows-in-all-frames): New function to prevent xlib error when a window is deleted.

src/clfswm-expose-mode.lisp (define-expose-letter-keys): Add 0..1 and A..Z keys to select a child in expos mode.

src/clfswm-internal.lisp (show-all-children): Rectangular optimization to display only needed children.

src/clfswm-configuration.lisp (query-conf-value): Add the ability to leave the field blank to reset the variable to its default value.

contrib/server/server.lisp: Load clfswm client code in the main program and let the user start it with a --client command line option. * src/package.lisp (*main-entrance-hook*): New hook executed after loading configuration file and before opening the display.

src/*.lisp: Replace the case to handle event with a more (tricky) lispy  method which bind a function to each keywords associated to graphics events. Remove event handler hooks as they're not needed anymore (To replace them: use closure and define-handler).

src/clfswm-internal.lisp (remove-child-in-frame): Do not destroy the frame window and the frame gc. Close a very annoying bug when cuting/pasting a frame or moving a child over frames with the mouse.

src/clfswm-util.lisp (mouse-click-to-focus-generic): Redisplay all children in *current-root* after moving/resizing a frame.

identify-key, move-window, resize-window, wait-mouse-button-release: Add a timeout in xlib:process-event.

src/clfswm.lisp (main): Add an alternate configuration filename parameter. load.lisp: Add a debuging code example.