matkerint versus matsnf

[Jeroen Demeyer <jdemeyer@cage.ugent.be>]

Hello pari-dev,

If I want to compute a Z-basis of the kernel of a matrix, the most 
obvious GP function would be matkerint().  However, that does a 
LLL-reduction which is not needed for my application.

The kernel of an integral matrix can also be found using matsnf().  In 
many cases, matsnf is faster if the matrix has more columns than rows 
(more unknowns than relations).

Considering this, I think that it makes sense to add a flag to 
matkerint() indicating that matsnf should be used.

Let me know what you think about this.

Cheers,
Jeroen.