[btcsuite/btcd] 2b2510: Add generation code for the endomorphism vectors.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/btcsuite/btcd
  Commit: 2b25107317ed533a6aaf8c80091a921ed0a43d6d
      
https://github.com/btcsuite/btcd/commit/2b25107317ed533a6aaf8c80091a921ed0a43d6d
  Author: Dave Collins <da...@conformal.com>
  Date:   2015-02-06 (Fri, 06 Feb 2015)

  Changed paths:
    M btcec/genprecomps.go
    M btcec/gensecp256k1.go

  Log Message:
  -----------
  Add generation code for the endomorphism vectors.

This commit adds code which generates the linearly independent vectors
used by the secp256k1 endomorphism code.  These value are hard-coded into
the curve already, but having the code used to generate them is handy
should any future curves be added which can also make use of the same
class of endomorphism.