Fix #1198, enable custom locale in template rendering, fixes links

reverts getpelican/pelican@ddcccfeaa9

If one used a locale that made use of unicode characters (like fr_FR.UTF-8)
the files on disk would be in correct locale while links would be to C.

Uses a SafeDatetime class that works with unicode format strigns
by using custom strftime to prevent ascii decoding errors with Python2.

Also added unicode decoding for the calendar module to fix period
archives.

pelican/tools/pelican_import.py

@@ -21,7 +21,7 @@ from six.moves.urllib.error import URLError
 from six.moves.urllib.parse import urlparse
 from six.moves.urllib.request import urlretrieve
 
-from pelican.utils import slugify
+from pelican.utils import slugify, SafeDatetime
 from pelican.log import init
 
 logger = logging.getLogger(__name__)
@@ -303,7 +303,7 @@ def dc2fields(file):
 def posterous2fields(api_token, email, password):
     """Imports posterous posts"""
     import base64
-    from datetime import datetime, timedelta
+    from datetime import timedelta
     try:
         # py3k import
         import json
@@ -340,7 +340,7 @@ def posterous2fields(api_token, email, password):
                 slug = slugify(post.get('title'))
             tags = [tag.get('name') for tag in post.get('tags')]
             raw_date = post.get('display_date')
-            date_object = datetime.strptime(raw_date[:-6], "%Y/%m/%d %H:%M:%S")
+            date_object = SafeDatetime.strptime(raw_date[:-6], "%Y/%m/%d %H:%M:%S")
             offset = int(raw_date[-5:])
             delta = timedelta(hours = offset / 100)
             date_object -= delta