Fix test errors on OSX

On OSX, if LC_TIME and LC_CTYPE differs the output of strftime is not properly decoded
in Python 3. This makes sure that the 'utils.DateFormatter' and the related Jinja filter
'strftime' set the same value for LC_TIME and LC_CTYPE while formatting.

Also, '%a' is removed from DEFAULT_DATE_FORMAT in 'custom_locale' tests. OSX and *nix have
different conversions for '%a' ('Jeu' vs 'jeu.') and there is not a feasible way to handle
the difference for tests.

samples/pelican_FR.conf.py

@@ -1,59 +0,0 @@
-# -*- coding: utf-8 -*-
-from __future__ import unicode_literals
-
-AUTHOR = 'Alexis Métaireau'
-SITENAME = "Alexis' log"
-SITEURL = 'http://blog.notmyidea.org'
-TIMEZONE = "Europe/Paris"
-
-# can be useful in development, but set to False when you're ready to publish
-RELATIVE_URLS = True
-
-GITHUB_URL = 'http://github.com/ametaireau/'
-DISQUS_SITENAME = "blog-notmyidea"
-PDF_GENERATOR = False
-REVERSE_CATEGORY_ORDER = True
-LOCALE = "fr_FR.UTF-8"
-DEFAULT_PAGINATION = 4
-DEFAULT_DATE = (2012, 3, 2, 14, 1, 1)
-
-ARTICLE_URL = 'posts/{date:%Y}/{date:%B}/{date:%d}/{slug}/'
-ARTICLE_SAVE_AS = ARTICLE_URL + 'index.html'
-
-FEED_ALL_RSS = 'feeds/all.rss.xml'
-CATEGORY_FEED_RSS = 'feeds/%s.rss.xml'
-
-LINKS = (('Biologeek', 'http://biologeek.org'),
-         ('Filyb', "http://filyb.info/"),
-         ('Libert-fr', "http://www.libert-fr.com"),
-         ('N1k0', "http://prendreuncafe.com/blog/"),
-         ('Tarek Ziadé', "http://ziade.org/blog"),
-         ('Zubin Mithra', "http://zubin71.wordpress.com/"),)
-
-SOCIAL = (('twitter', 'http://twitter.com/ametaireau'),
-          ('lastfm', 'http://lastfm.com/user/akounet'),
-          ('github', 'http://github.com/ametaireau'),)
-
-# global metadata to all the contents
-DEFAULT_METADATA = (('yeah', 'it is'),)
-
-# path-specific metadata
-EXTRA_PATH_METADATA = {
-    'extra/robots.txt': {'path': 'robots.txt'},
-    }
-
-# static paths will be copied without parsing their contents
-STATIC_PATHS = [
-    'pictures',
-    'extra/robots.txt',
-    ]
-
-# custom page generated with a jinja2 template
-TEMPLATE_PAGES = {'pages/jinja2_template.html': 'jinja2_template.html'}
-
-# code blocks with line numbers
-PYGMENTS_RST_OPTIONS = {'linenos': 'table'}
-
-# foobar will not be used, because it's not in caps. All configuration keys
-# have to be in caps
-foobar = "barbaz"