avoid encoding problems when handling unicode strings from sqlite db

[mir06]

using python 2.X the the format strings must be marked as unicode, because sqlite delivers utf-8 strings

string = u'groß' 
"{}".format(string)
UnicodeEncodeError: 'ascii' codec can't encode character u'\xdf' in position 3: ordinal not in range(128)

string = u'groß' 
u"{}".format(string)
u'gro\xdf'
u"{}".format(string).encode('utf-8')
'gro\xc3\x9f'

[coveralls]

Coverage remained the same at 95.882% when pulling ecb4145 on mir06:sqlite-utf8 into a34f81b on django-dbbackup:master.

[ZuluPro]

Hello @mir06
Sorry for my latency, I just see your PR,
After fix, I'll merge it soon.

[mir06]

@ZuluPro don't worry, thanks for your package

[ZuluPro]

Hello @mir06,

I can't accept your solution because it won't work with python 3.2,
And we want dbbackup to help devs to get out from this version :D

I fix it by put from __future__ import unicode_literals, simply...
And added a test about it.
You'll have this fix in 3.1.1, very soon.

Thanks for your work and do not hesitate to open an issue if it isn't resolved for you.

[mir06]

@ZuluPro well, yes that's more elegant 😄