Use unidecode to improve image filenames (fix#136)

Image filenames containing non ascii characters would be translated to a
series of underscores (____.png). To fix this, we use the unidecoe library
(which we also add to the required packages for Wagtail) which translates
each unicode character to an ascii equivalent.

For more info on how unidecode works please check @Evgeny's answer at this
question:

http://stackoverflow.com/questions/702337/how-to-make-django-slugify-work-properly-with-unicode-strings

setup.py

@@ -48,6 +48,7 @@ setup(
         "Pillow>=2.3.0",
         "beautifulsoup4>=4.3.2",
         "lxml>=3.3.0",
+        'Unidecode>=0.04.14',
         "BeautifulSoup==3.2.1",  # django-compressor gets confused if we have lxml but not BS3 installed
     ],
     zip_safe=False,

wagtail/wagtailimages/models.py

@@ -14,6 +14,8 @@ from django.utils.html import escape
 from django.conf import settings
 from django.utils.translation import ugettext_lazy  as _
 
+from unidecode import unidecode
+
 from wagtail.wagtailadmin.taggable import TagSearchable
 from wagtail.wagtailimages import image_ops
 
@@ -25,8 +27,9 @@ class AbstractImage(models.Model, TagSearchable):
         folder_name = 'original_images'
         filename = self.file.field.storage.get_valid_name(filename)
 
+        # do a unidecode in the filename and then
         # replace non-ascii characters in filename with _ , to sidestep issues with filesystem encoding
-        filename = "".join((i if ord(i) < 128 else '_') for i in filename)
+        filename = "".join((i if ord(i) < 128 else '_') for i in unidecode(filename))
 
         while len(os.path.join(folder_name, filename)) >= 95:
             prefix, dot, extension = filename.rpartition('.')