Fix decoding of Cursor.description column names. Fixes #190 - The issue was a column alias with an i with acute which caused an error. pyodbc now (1) uses the Unicode version of SQLDescribeColumn and (2) uses the configured SQL_C_WCHAR encoding. I've added SQL Server test decode_meta for this.
When a connection is used in a with clause (as a context manager), the connection has always been committed if successful. However, when an exception is raised it now issues a specific rollback. In the past neither was performed if an exception was raised.