ENH: WLS log-like now matches GLS for comparable weights
TST: adjust test WLS llf, aic, bic because of different definition
TST add test comparing WLS, GLS, rsquared differs see #1252
Merge pull request #1253 from josef-pkt/WLS-llf-fix

REF Wls llf fix closes #1170 closes #1251
TST: enable tests for llf after change to WLS.loglike see #1170
Merge pull request #1192 from josef-pkt/enable_WLS_llf_tests

TST: enable tests for llf for GLSAR
BUG: Fixes issue #347: nobs check in Granger test
TST/STY: add test for ValueError, code cleanup
Merge branch 'granger-cleanup-and-nobs-check' BUG closes #347 closes #1018