Some tweaks to make grunt faster.
Some tweaks to make grunt faster.

The big hard part for the algorithm is the sieving with the regexp I'm
using ... about printing is behaving pretty much ok, so I can't complain
about it, still I couldn't put the times below the minute.

In average, this is the time I get: 1' 42.001''

darkturo/primo,darkturo/primo,darkturo/primo