convert internal representation of AntiFeatures to list

The AntiFeatures metadata is a comma-separated list of tags, like
Categories, so it should also be stored internally as a list.  This makes
parsing XML and JSON easier.

The test cases' .pickle files look like they change a lot, but they really
don't, its only the change of default AntiFeatures value from None to []

fdroidserver/metadata.py

@@ -42,7 +42,7 @@ class MetaDataException(Exception):
 # In the order in which they are laid out on files
 app_defaults = OrderedDict([
     ('Disabled', None),
-    ('AntiFeatures', None),
+    ('AntiFeatures', []),
     ('Provides', None),
     ('Categories', ['None']),
     ('License', 'Unknown'),
@@ -516,7 +516,7 @@ def read_metadata(xref=True):
 def metafieldtype(name):
     if name in ['Description', 'Maintainer Notes']:
         return 'multiline'
-    if name in ['Categories']:
+    if name in ['Categories', 'AntiFeatures']:
         return 'list'
     if name == 'Build Version':
         return 'build'
@@ -929,7 +929,7 @@ def write_metadata(dest, app):
 
     mf = open(dest, 'w')
     writefield_nonempty('Disabled')
-    writefield_nonempty('AntiFeatures')
+    writefield('AntiFeatures')
     writefield_nonempty('Provides')
     writefield('Categories')
     writefield('License')

fdroidserver/stats.py

@@ -256,8 +256,7 @@ def main():
     for app in metaapps:
         if app['AntiFeatures'] is None:
             continue
-        antifeatures = [a.strip() for a in app['AntiFeatures'].split(',')]
-        for antifeature in antifeatures:
+        for antifeature in app['AntiFeatures']:
             afs[antifeature] += 1
     with open('stats/antifeatures.txt', 'w') as f:
         for antifeature, count in afs.most_common():

fdroidserver/update.py

@@ -92,8 +92,8 @@ def update_wiki(apps, sortedids, apks):
         wikidata = ''
         if app['Disabled']:
             wikidata += '{{Disabled|' + app['Disabled'] + '}}\n'
-        if app['AntiFeatures']:
-            for af in app['AntiFeatures'].split(','):
+        if 'AntiFeatures' in app:
+            for af in app['AntiFeatures']:
                 wikidata += '{{AntiFeature|' + af + '}}\n'
         wikidata += '{{App|id=%s|name=%s|added=%s|lastupdated=%s|source=%s|tracker=%s|web=%s|changelog=%s|donate=%s|flattr=%s|bitcoin=%s|litecoin=%s|dogecoin=%s|license=%s|root=%s}}\n' % (
             appid,
@@ -847,7 +847,7 @@ def make_index(apps, sortedids, apks, repodir, archive, categories):
         addElement('marketvercode', app['Current Version Code'], doc, apel)
 
         if app['AntiFeatures']:
-            af = app['AntiFeatures'].split(',')
+            af = app['AntiFeatures']
             if af:
                 addElementNonEmpty('antifeatures', ','.join(af), doc, apel)
         if app['Provides']: