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/utils.py

@@ -14,6 +14,7 @@ import shutil
 import traceback
 import pickle
 import hashlib
+import datetime
 
 from collections import Hashable
 from contextlib import contextmanager
@@ -56,7 +57,10 @@ def strftime(date, date_format):
     for candidate in candidates:
         # test for valid C89 directives only
         if candidate[1] in 'aAbBcdfHIjmMpSUwWxXyYzZ%':
-            formatted = date.strftime(candidate)
+            if isinstance(date, SafeDatetime):
+                formatted = date.strftime(candidate, safe=False)
+            else:
+                formatted = date.strftime(candidate)
             # convert Py2 result to unicode
             if not six.PY3 and enc is not None:
                 formatted = formatted.decode(enc)
@@ -68,6 +72,17 @@ def strftime(date, date_format):
     return template % tuple(formatted_candidates)
 
 
+class SafeDatetime(datetime.datetime):
+    '''Subclass of datetime that works with utf-8 format strings on PY2'''
+
+    def strftime(self, fmt, safe=True):
+        '''Uses our custom strftime if supposed to be *safe*'''
+        if safe:
+            return strftime(self, fmt)
+        else:
+            return super(SafeDatetime, self).strftime(fmt)
+
+
 class DateFormatter(object):
     '''A date formatter object used as a jinja filter
 
@@ -183,8 +198,10 @@ def get_date(string):
     If no format matches the given date, raise a ValueError.
     """
     string = re.sub(' +', ' ', string)
+    default = SafeDatetime.now().replace(hour=0, minute=0,
+                                        second=0, microsecond=0)
     try:
-        return dateutil.parser.parse(string)
+        return dateutil.parser.parse(string, default=default)
     except (TypeError, ValueError):
         raise ValueError('{0!r} is not a valid date'.format(string))