title: pymssql callproc unicode - returns an error
body: <p>I need help on calling "sp_executesql" via callproc (i need it as RPC). this is my code:</p>
  
  <pre><code>import pymssql
  conn = pymssql.connect(host='11.22.33.44:1433', user='sa', password='XYZ', database='AdventureWorks')
  cur = conn.cursor()
  cur.callproc("sp_executesql", 'SELECT * FROM AdventureWorks.HumanResources.Employee WHERE BusinessEntityID = 109')
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>  File "executesql.py", line 4, in &lt;module&gt;
      cur.callproc("sp_executesql", 'SELECT * FROM AdventureWorks.HumanResources.Employee WHERE BusinessEntityID = 109')
    File "pymssql.pyx", line 357, in pymssql.Cursor.callproc (pymssql.c:4238)
      self._returnvalue = proc.execute()
    File "_mssql.pyx", line 1289, in _mssql.MSSQLStoredProcedure.execute (_mssql.c:12177)
      check_cancel_and_raise(rtc, self.conn)
    File "_mssql.pyx", line 1322, in _mssql.check_cancel_and_raise (_mssql.c:12473)
      return maybe_raise_MSSQLDatabaseException(conn)
    File "_mssql.pyx", line 1366, in _mssql.maybe_raise_MSSQLDatabaseException (_mssql.c:13067)
      raise ex
  _mssql.MSSQLDatabaseException: (214, "Procedure expects parameter '@statement' of type 'ntext/nchar/nvarchar'.DB-Lib error message 214, severity 16:\nGeneral SQL Server error: Check messages from the SQL Server\n")
  </code></pre>
  
  <p>Running other stored procedures goes smoothly.
  Running the string as unicode (u'Select...') gives this error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "executesql.py", line 4, in &lt;module&gt;
      cur.callproc("sp_executesql", u'SELECT * FROM AdventureWorks.HumanResources.Employee WHERE BusinessEntityID = 109')
    File "pymssql.pyx", line 354, in pymssql.Cursor.callproc (pymssql.c:4177)
      raise NotSupportedError('Unable to determine database type')
  pymssql.NotSupportedError: Unable to determine database type
  </code></pre>
  
  <p>Do you know how to overcome this?</p>
  
  <p>SQL Server is 
  Microsoft SQL Server 2012 - 11.0.2100.60 (X64)   Feb 10 2012 19:39:15   Copyright (c) Microsoft Corporation  Enterprise Edition (64-bit) on Windows NT 6.1  (Build 7601: Service Pack 1) (Hypervisor) </p>
  
  <p>Thanks a lot</p>