Use AC_CONFIG_HEADERS instead of AM_CONFIG_HEADER to appease automake 1.13

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
test: add a dlclose test

Closing an X display that had a VDPAU device created on it causes a crash.

Work around an identical libXext dlclose bug with the "Generic Event Extension"
by dlopening libXext.so.6 and leaving it open.

Original bug discovered and fixed by Robert Morell <rmorell@nvidia.com> in
commit 3b43955c7324e1d213a3134387767722f34e2356.

v2: Don't SKIP if creating the device fails.  Just attempting to create the
device installs the DRI2 extension that causes the problem.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Robert Morell <rmorell@nvidia.com>