Fix for issue #13 + 2 new cpuminer features

The fix for the issue #13 is the third commit.

scrypt:512 tested on Vertcoin, stratum+tcp://eu.vert.geek.nz:9171
x14 tested on stratum+tcp://www.hashharder.com:9672
x13 seems slower, tested on ./minerd -t 4 -o stratum+tcp://www.hashharder.com:9633 --algo=x13

currently working on x15