Use subscript syntax in tag archive generation

Using dot caused jinja to fail if the tag contained
characters such as '-' or spaces.

hyde/ext/plugins/tagger.py

@@ -198,7 +198,7 @@ extends: false
 
 {%% set tag = site.tagger.tags['%(tag)s'] %%}
 {%% set source = site.content.node_from_relative_path('%(node)s') %%}
-{%% set walker = source.walk_resources_tagged_with_%(tag)s %%}
+{%% set walker = source['walk_resources_tagged_with_%(tag)s'] %%}
 {%% extends "%(template)s" %%}
 """
         for tagname, tag in self.site.tagger.tags.to_dict().iteritems():
@@ -212,4 +212,4 @@ extends: false
             archive_file = File(target.child("%s.%s" % (tagname, extension)))
             archive_file.delete()
             archive_file.write(text.strip())
-            self.site.content.add_resource(archive_file)
+            self.site.content.add_resource(archive_file)