[eigen] Eigen::Complex attempt

[Mark Borgerding <mark@xxxxxxxxxxxxxx>]

I just started out by trying to see if I could make the Complex class 
have an operator & which returns a "pointer object" that could be 
converted to either
Eigen::Complex<T> *
or
std::complex<T> *
That worked and then I just didn't know when to quit.  So now here is a 
Complex class that has a superset of the std::complex interface and 
actually uses std::complex whenever it can.  It has more accessors and 
mutators.

http://bitbucket.org/mborgerd/eigen2_for_fft/src/tip/unsupported/Eigen/Complex

Note the structure packing should be identical (assuming the C++ 
standards folks are correct in their assessment that "All existing 
implementations already have the layout proposed here."  
http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#387 )

-- Mark