Increase slug size from 50 to 255.

In edx-platform, default course wiki article's slug is automatically set
to "{org}.{number}.{run}", which can be more than 50 characters long.

The wiki breaks if the automatically assigned slug is longer than 50
characters.

We usually use 255 character size for columns that store course_key in
edx-platform, so I believe it makes sense to use a limit of 255 for wiki
slugs, too.

setup.py

@@ -29,7 +29,7 @@ package_data = dict(
 
 setup(
     name = "django-wiki",
-    version = "0.0.8",
+    version = "0.0.9",
     author = "Benjamin Bach",
     author_email = "benjamin@overtag.dk",
     description = ("A wiki system written for the Django framework."),

wiki/migrations/0004_increase_slug_size.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('wiki', '0003_ip_address_conv'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='urlpath',
+            name='slug',
+            field=models.SlugField(max_length=255, null=True, verbose_name='slug', blank=True),
+        ),
+    ]

wiki/models/urlpath.py

@@ -41,7 +41,9 @@ class URLPath(MPTTModel):
     article = models.ForeignKey(Article, on_delete=models.CASCADE, editable=False,
                                 verbose_name=_(u'Cache lookup value for articles'))
     
-    SLUG_MAX_LENGTH = 50
+    # The slug is constructed from course key and will in practice be much shorter then 255 characters
+    # since course keys are capped at 65 characters in the Studio (https://openedx.atlassian.net/browse/TNL-889).
+    SLUG_MAX_LENGTH = 255
     
     slug = models.SlugField(verbose_name=_(u'slug'), null=True, blank=True,
                             max_length=SLUG_MAX_LENGTH)