Feature request: add ec_check

[asomers]

ISA-L's raid module includes the parity check functions xor_check and pq_check for verifying parity. But there's no equivalent in the erasure code module. Could we please have a general parity check function like int ec_check(int len, int k, int rows, unsigned char *gftbls, unsigned char **data)? Or perhaps a pair of functions, one that takes precalculates a parity check matrix, and one that uses it to verify parity?

[gbtucker]

Thanks Alan, we'll look into it.