ENH: Use sqlalchemy for PostGIS connection for better compatibility with pandas.read_sql
ENH: Take either SQLalchemy engine or a DB API connection object
TST: Update the tests to use SQLalchemy for new pandas and DB API for older pandas versions
TST: Add SQLAlchemy to test requirements
TST CLN: Remove repeated import
Merge branch 'master' into bug/pandas-sqlalchemy-no-travis

Conflicts:
	requirements.test.txt
TST: Skip on OperationalError for newer pandas versions
TST: Don't raise in utility function
TST: Don't depend on OperationalError for exceptions in connecting to test database
TST BUG: We still need OperationalError import
Merge pull request #123 from geopandas/bug/pandas-sqlalchemy-no-travis

Use SQLAlchemy engine on pandas >= 0.14.0