err_handler: Don't clobber dberrstr with oserrstr

The error handler was tending to use the oserrstr and not the dberrstr,
resulting in error messages like this:

    pymssql.OperationalError: (20009, 'Net-Lib error during Connection
    refused')

With this change, the dberrstr is also included resulting in:

    pymssql.OperationalError: (20009, 'DB-Lib error message 20009,
    severity 9:\nUnable to connect: Adaptive Server is unavailable or
    does not exist\nNet-Lib error during Connection refused\n')
Merge pull request #151 from pymssql/err_handler_dont_clobber_dberrstr_with_oserrstr

err_handler: Don't clobber dberrstr with oserrstr
test_utils.py: Remove unnecessary import

of nose.plugins.skip.SkipTest
test_utils.py: from _mssql import substitute_params
test_utils.py: Convert methods to functions

Change from unittest-style test class to nosetests/py.test style test
functions
_mssql.pyx: Fix minor typos/formatting in comments
test_utils.py: Improve pep8 and pylint compliance
Mark testErrorSprocThreadedUse as a slow test
tests/helpers.py: pep8 and pylint improvements
Add test_as_dict_no_column_name, test_as_dict_no_column_name_2

Add tests for when as_dict=True and columns missing names.
execute: Raise ColumnsWithoutNamesError when as_dict=True and missing
column names
faq.rst: Fix a few typos
ChangeLog: Fix minor typo; uniqueidentifer => uniqueidentifier
Add docs: Migrating from 1.x to 2.x
Merge pull request #160 from pymssql/as_dict_No_column_name_raise_exception2

Raise exception if as_dict=True and column(s) have no names
Merge pull request #162 from pymssql/docs_migrate_1_x_to_2_x

Add docs: Migrating from 1.x to 2.x
migrate_1_x_to_2_x.rst: Fix typo
faq.rst: Mention as dict=True and columns without names
Merge pull request #164 from pymssql/faq_mention_as_dict_True_and_columns_without_names

faq.rst: Mention as dict=True and columns without names
faq.rst: Mention DATE and TIME unserialized to str

pymssql does not unserialize ``DATE`` and ``TIME`` columns to
``datetime.date`` and ``datetime.time`` instances