[ntl] ntl v8 - exceptions!

[Victor Shoup]

I finally transformed the internals of NTL to be exception safe and to throw
exceptions upon encountering an error (rather than the old "abort with error message"
approach).

This required a major overhaul of a lot of NTL internals, but the high level
interfaces remain unchanged.

To enable exceptions, you need to configure with NTL_EXCEPTIONS=on,
and use a C++11 compiler (you need "lambdas" and C++11-style "noexcept").

Unfortunately, error handling in GMP is still rather crude, and so the 
usefulness of all this is a bit limited if NTL is built using GMP.  That said,
the GMP developers are planning on adding proper error handling...hopefully soon.

More details:
http://www.shoup.net/ntl/doc/tour-changes.html
http://www.shoup.net/ntl/doc/tour-struct.html#except

Happy holidays!!

----
Prof. Victor Shoup
Dept. of Computer Science
New York University