* src/xwidget.c: Fix a lot of errors when compiling with --enable-checking
and --enable-check-lisp-object-type.
* src/xwidget.h (XXWIDGET): XXWIDGET expects a PSEUDOVECTOR not a display
spec.
* src/xwidget.c (Fmake_xwidget): Store xwidget in Vxwidget_list.
(syms_of_xwidget): Rename Vxwidget_alist to Vxwidget_list and register
`get-buffer-xwidgets' as a new subr.
(Fget_buffer_xwidgets): New function to return a list of xwidgets attached
to the specified buffer.
Handle xwidgets like processes and delete them when their buffer is killed.

* lisp/xwidget.el (xwidget-kill-buffer-query-function): New function to
query a user before killing a buffer with xwidgets in it.

This function is stored in `kill-buffer-query-functions' and called from
`kill-buffer'.
* src/buffer.c (Fkill_buffer): Call `kill_buffer_xwidgets'.
* src/xwidget.c (kill_buffer_xwidgets): Delete xwidgets attached to the
specified buffer.
* src/xwidget.h (kill_buffer_xwidgets): Add definition.
Merge pull request #3 from daimrod/fix-compile-time-errors

Fix compile time errors
Merge pull request #4 from daimrod/Vxwidget_list

Vxwidget list