Added handler for SIGABRT
compositor: Remove unused wl_pointer variable

Using move_pointer() in notify_pointer_focus() left the wl_pointer variable
unused.
build: Make the X11 compositor explicitely depend on xcb-shm

Otherwise, it means the X11 compositor depends on another library to
pull xcb-shm (cairo?), which is not always the case. Here I end up with:

[01:54:38.970] Failed to load module:
$prefix/lib/weston/x11-backend.so: undefined symbol: xcb_shm_id
sdk: be C++ friendly

This renames the weston_surface's private member to configure_private
and externs "C" the headers of the SDK.
gitignore: Ignore test-driver

Automake (1.12 here) parallel-tests installs a test-driver file, another
file to add to .gitignore.

While at it, remove the duplicate cscope.out entry and add TAGS (the
result of automake's "make tag")
compositor: add WESTON_COMPOSITOR_OFFSCREEN state

This state is used when the user switches the vt. It turns of rendering
and frame events, but doesn't set the DPMS state to off.

As a part of this change, also turn off the idle timer when entering
the SLEEPING or OFFSCREEN states, which fixes
https://bugs.freedesktop.org/show_bug.cgi?id=61910 (rpi backend
untested).