CVE 2010-4352: Reject deeply nested variants

CVE 2010-4352: Reject deeply nested variants

Add DBUS_INVALID_NESTED_TOO_DEEPLY validity problem and a test that
should generate it.

Previously, we rejected deep nesting in the signature, but
variants allow dynamic message nesting, conditional only
on the depth of the message body.

The nesting limit is 64, which was also the limit in static
signatures.  Empirically, dynamic nesting depth observed on my
Fedora 14 system doesn't exceed 2; 64 is really a huge limit.

https://bugs.freedesktop.org/show_bug.cgi?id=32321

Signed-Off-By: Colin Walters <walters@verbum.org>
Signed-off-by: Will Thompson <will.thompson@collabora.co.uk>
Conflicts:

	dbus/dbus-marshal-validate.h