TST "confusion_matrix" was a duplicated key in CLASSIFICATION_METRICS and NOT_SYMMETRIC_METRICS dicts
TST style fix: old_error_settings should be outside try-finally block to be safely used in finally statement
FIX classification_report shouldn't fail on unicode labels in Python 2.x

'{0}'.format(arg) doesn't promote the whole string to unicode if arg is unicode - it tries to encode arg to sys.getdefaultencoding() instead.
"%s" doesn't have this gotcha.
Merge pull request #2462 from kmike/metrics-unicode

[MRG] Add unicode support to sklearn.metrics.classification_report