Add parsing of 'noexcept' keyword

Teach Shiboken to parse the 'noexcept' keyword. This doesn't add any
features (and we only support unconditional 'noexcept' for now), but
addresses an internal error that causes shiboken to SEGV trying to parse
modern versions of boost::intrusive_ptr. A test case to replicate the
crash (without the other changes) is also added.

Change-Id: I4713593dfd189c02ef4a2d7447d785b6d378019c
Reviewed-by: John Ehresman <jpe@wingware.com>