Add a bench-mode to sieve executable.
Add a bench-mode to sieve executable.

Typical usage: ./sieve param.2.607 -bench 23-26 .
This gives an estimation of the number of relations and of the runtime
for the whole set of special-q of degree 23 to 26.
The relevant information can be grep'd in the output with the BENCH keyword.

mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs