ENH: Option to avoid "center" environment.
ENH: Avoid RuntimeWarning when hessian unused
TST: Remove unnecessary test.
Merge pull request #1543 from jseabold/tst-fix-warning

TST: Suppress RuntimeWarning for L-BFGS-B
CLN: Improve warnings to avoid generic warnings messages

All generic Warnings have been replaced with specific warnings, which have
been consolidated into sm_exceptions.py.

Conflicts:
	statsmodels/tools/sm_exceptions.py
Added specific warnings in a couple of places where they were missing

Converted raise Warning to warning.warn

Made certain warnings had been imported in some modules where it was lazily
imported

Simplified warnings in GEE which was neither lazily imported nor imported
at the top of the file
Fix for conda 3.4 changes
Merge pull request #1510 from bashtage/warning-convert

CLN: Improve warnings to avoid generic warnings messages
Merge pull request #1544 from bashtage/travis-miniconda

MAINT: Fix travis miniconda build
Merge pull request #1438 from toobaz/uncentered_table

ENH: Option to avoid "center" environment.