Fix formatter of auto-installed logging handler.

[CruzR]

Formatter objects in Python 3.2+ support .format()-style format strings
if constructed with the style parameter set to '{', but that was never
backported to Python 2.7.

[wpercy]

Just to make sure I'm on the right page here, this is a backwards-compatibility fix for Python 2.7, correct?

[CruzR]

No, the old code was also broken for Python 3. By default, Formatter objects expect to be constructed with a %-style format string, even in Python 3. In Python 3.2+, the constructor has an additional parameter called style that can be set to '{' to allow .format-style format strings, but since that was never backported, I went with the %-style format string.

[CruzR]

In case you want to reproduce the issue, run

python -m unittest tests.TestGeneralFileParsing.test_bad_line

with and without this commit. Without it, you should see the literal format string without any variable interpolation being printed to stderr, with it the correct error message about an unreadable line being skipped should appear.

[wpercy]

Looks good to me. I'll merge it in and see if there are any other issues I can knock out before I deploy to pypi.

[CruzR]

I'm currently trying to figure out whether I can implement VCard 2.1 support, so if you want to hold off a couple more days, you could avoid deploying to pypi twice.

[wpercy]

Sounds good, thanks for the heads up. I'll hold off til next week.

[CruzR]

vCard 2.1 is quite painful, looks like I won't be implementing support for it this week.