ENH: add use_t to LikelihoodModelResults pvalues and confint closes #1812
BUG: GLMResults.summary fix use_t closes #1829
BUG: summary2 use use_t from results closes #1828
REF RLM, discrete summary, use_t from results
REF: add use_t as class attribute
Merge pull request #1830 from josef-pkt/use-t_issue1812

BUG/ENH Use t in LikelihoodModelResults