better handling for byte strings that don't represent ascii data about pymssql

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I have a pymssql only tests now for this in test_types.py:TestTypes.test_image. 
 There is also a commit in [bea17389d31e] which fixes this problem from a 
technical standpoint.  It simply turns all type(str) values into a hex 
representation and sends that to MSSQL.  This seems to work well from a 
technical perspective.

However, the down-side is that it makes debugging difficult.  If someone is 
trying to debug a problem by watching SQL Server traces, they are only going to 
see the hex coming over.  Since character data will probably be the most common 
type(str) to be sent over, this seems unideal.

Therefore, in [5ba20a7b7d70] I made the quote function smarter so that anything 
that can be decoded as ascii will get put directly in the string.  Everything 
else gets hex encoded.

These changes are currently in my bb repo but I would appreciate a look over 
what I have done to make sure it looks good.

Original comment by [email protected] on 16 Apr 2011 at 5:37

• Changed title: better handling for byte strings that don't represent ascii data
• Changed state: Fixed