64bit variant naming scheme

[Takeshi Enomoto]

I think scientific users want not universal (i386 and ppc) but 64-bit   
(x86_64 and ppc64)
if they have a 64-bit machine.

If a package is build for all the four (i386 x86_64 ppc ppc64),
there will be not problem but it is not always easy to support this.

For example source in fortran is problematic.
gfortran in gcc43 -m64 option but not -arch x86_64 or ppc64.
To build universal one needs to go through build process twice with - 
m32 and -m64
and use lipo later.
I have not yet able to provide g95 64-bit.

My point is building for two types of cpus and for 32/64 bit are not  
always the same
and an average scientific user wants 64 bit version for the host (her/ 
his local) machine.

A universal Portfile has been posted for fftw-3, which is under  
examination.
<https://trac.macports.org/ticket/13814>
It would be nice if port command itself have a similar function.

Otherwise it would be nice to enable the user to choose 32/64 bit.

Takeshi