ENH: add cov_type to Regression model.fit(), first version
DOC: covtype in fit: update example with cluster
BUG: use use_t argument
REF: base Model, new optional attribute df_resid_inference
TST: robustcov add test for fit options and for scale, rsquared
     fix example
Merge pull request #1867 from josef-pkt/REF_covtype_fit

ENH/REF add covtype choice to fit method
TST: fix _infer_freq for pandas .14+ compat

pandas 0.14 fixed a bug with DatetimeIndex's
freqstr attribute. Previously relied on
having the freqstr attribute implying that freqstr
was not none.
Merge pull request #1872 from TomAugspurger/infer_freq_pandas_break

BUG: fix _infer_freq for pandas .14+ compat closes #1822
BUG: add _ctor_param to TransfGen distributions

so that they can be frozen with scipy >= 0.14.
see scipy gh-3852, statsmodels gh-1865
Merge pull request #1883 from ev-br/frozen_transf

BUG: add _ctor_param to TransfGen distributions closes #1864
Fix: Add compat code for pd.Categorical in pandas>=0.15
TST: corr_nearest_factor, add test for sparse svds, objective values
Merge pull request #1884 from JanSchulz/cat_fixes

BUG: Add compat code for pd.Categorical in pandas>=0.15
Merge pull request #1885 from josef-pkt/corr_nearest_factor_1850

TST: corr_nearest_factor, more informative tests
BUG pandas 0.15 compatibility in grouputils labels
Merge pull request #1886 from josef-pkt/BUG_grouputils_pandas_compat

BUG pandas 0.15 compatibility in grouputils labels
ENH: add tools.testing module for asserts (numpy, pandas compat wrapper)
TST: pandas compat: change asserts (failing with pandas master for 0.15)
TST test_corrpsd Test_Factor: add noise to data
Merge pull request #1888 from josef-pkt/corr_nearest_factor_1850_4

TST test_corrpsd Test_Factor: add noise to data