fix get_db_prep_value when value is unicode

[zebuline]

No description provided.

[luto]

This PR really boils down to this line:

- if isinstance(value, str):
+ if isinstance(value, basestring):

The hyphenate-issue was already fixed (see #36).

Could you please re-submit a PR only contaning this change, since this PR has conflicts or tell me if this issue has been resolved?

[jaredlewis]

Any timetable on getting this merged? This is a flaw and is occurring for me in python 3.4

[micahhausler]

Rather than using basestring, can this use six.string_types?

[zebuline]

New PR here: #45