SAGE's multivariate gcd sucks over QQ and/or ZZ

[was]

I think those timings are way out of date, since Singular 3 seems
to be *very* fast at mod p multivariate GCD computation, even
though it sucks over QQ.   Check out this paper:

          http://www.cecm.sfu.ca/CAG/papers/brown.ps

It on exactly the problem of GCD over QQ (or equiv ZZ),
and section 2 has a complete description of a gcd algorithm 
that reduces gcd over ZZ to doing gcd's mod p.

Who wants to be a hero -- like Jon Bober and number of partitions -- 
and implement this for Sage, so that multivariate GCD's aren't 
embarrassingly slow in Sage anymore?   This slowness *has* 
been something reported to me on several occasions during 
the last 2 years. 

William

NOTE -- I would implement this modular GCD algorithm in Sage, not Singular.

I would also investigate other algorithms mentioned in the paper.

[was]

See #694 instead!