improved sqlalchemy test config handling
Set rowcount correctly after retrieving all rows through fetchall or fetchmany

ref #141
Added test created for PR #247

They use a different SQL query with no results.

They fail in the ``eq_(cur.rowcount, -1)`` assertions.
Merge branch 'pr280_more_tests' of git@github.com:pymssql/pymssql.git

Conflicts:
	tests/helpers.py
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