Logistic regression: Fixed a minor problem with direction restart in cg
Logistic regression: Fixed a minor problem with direction restart in cg

Jira: MADLIB-574

In the conjugate gradient method, the direction is restarted when
Polak-Ribière's beta <= 0 instead of <0.

Reason: In the Polak-Ribière (PR) fomula, beta is chosen as max(0,PR'beta),
so Hestenes-Stiefel's (HS) beta needs to be 0 when PR's beta <= 0 (not <0).
Otherwise, without the "=", HS's beta will blow up at the optimum solution.

Instead of comparing with 0, a small number is used.

njayaram2/madlib,hpandeycodeit/incubator-madlib,lmatthieu/incubator-madlib,apache/incubator-madlib,mktal/incubator-madlib,orhankislal/incubator-madlib,apache/incubator-madlib,apache/incubator-madlib,madlib/madlib,iyerr3/incubator-madlib,njayaram2/madlib,hpandeycodeit/incubator-madlib,rashmi815/incubator-madlib,orhankislal/madlib,iyerr3/incubator-madlib,lmatthieu/incubator-madlib,mktal/incubator-madlib,apache/incubator-madlib,cooper-sloan/incubator-madlib,cooper-sloan/incubator-madlib,iyerr3/incubator-madlib,rashmi815/incubator-madlib,cooper-sloan/incubator-madlib,iyerr3/incubator-madlib,rvs/incubator-madlib,mktal/incubator-madlib,orhankislal/incubator-madlib,iyerr3/incubator-madlib,orhankislal/madlib,hpandeycodeit/incubator-madlib,madlib/madlib,njayaram2/madlib,njayaram2/incubator-madlib,rashmi815/incubator-madlib,njayaram2/incubator-madlib,njayaram2/madlib,rashmi815/incubator-madlib,hpandeycodeit/incubator-madlib,njayaram2/incubator-madlib,lmatthieu/incubator-madlib,rvs/incubator-madlib,cooper-sloan/incubator-madlib,rvs/incubator-madlib,lmatthieu/incubator-madlib,orhankislal/madlib,orhankislal/incubator-madlib,rvs/incubator-madlib,orhankislal/incubator-madlib,hpandeycodeit/incubator-madlib,mktal/incubator-madlib,njayaram2/incubator-madlib,madlib/madlib,rashmi815/incubator-madlib,orhankislal/incubator-madlib,apache/incubator-madlib,rvs/incubator-madlib,njayaram2/incubator-madlib,madlib/madlib,madlib/madlib,mktal/incubator-madlib,orhankislal/madlib,lmatthieu/incubator-madlib,njayaram2/madlib,orhankislal/madlib,cooper-sloan/incubator-madlib