Use relative imports

This change does not affect to any behaviors of it, but is just stylish
improvements to remove 2to3 dependency.

1. All old-style absolute imports e.g. `from alembic import util` are
   replaced by relative imports e.g. `from . import util`.

2. Use of proxy modules (`alembic.op` and `alembic.context`) are replaced
   by deferred import patterns, but these modules still exist.

3. Imports are grouped by 3 types of their origins (standard libraries,
   third party libraries, and local modules) and blank lines are put between
   each group of imports.  This style is from PEP 8:

   <http://www.python.org/dev/peps/pep-0008/#imports>

For stylish change, I can't do that much, because it was intentionally done
as it was by the author.  If the author will allow me to make it more closer
to PEP 8 style, I will do that as well.

1 files changed, 7 insertions, 4 deletions

diff --git a/tests/test_mssql.py b/tests/test_mssql.py
index 66cdb9a..398d228 100644
--- a/tests/test_mssql.py
+++ b/tests/test_mssql.py
@@ -1,11 +1,14 @@
 """Test op functions against MSSQL."""
 from __future__ import with_statement
-from tests import op_fixture, capture_context_buffer, \
+
+from unittest import TestCase
+
+from sqlalchemy import Integer, Column
+
+from alembic import op, command, util
+from . import op_fixture, capture_context_buffer, \
     _no_sql_testing_config, assert_raises_message, staging_env, \
     three_rev_fixture, clear_staging_env
-from alembic import op, command, util
-from sqlalchemy import Integer, Column
-from unittest import TestCase
 
 
 class FullEnvironmentTests(TestCase):