add plugin tag type/comments and tag some pages.

I did this because I was looking for a summary/overview of the
various comment plugins that exist and couldn't already find
one.  I've tried to tag plugins that are mostly for use with
comments, which is a bit of a wide net and people may draw the
line in different places to myself.

doc/plugins/anonok.mdwn

@@ -1,5 +1,5 @@
 [[!template id=plugin name=anonok author="[[Joey]]"]]
-[[!tag type/auth]]
+[[!tag type/auth type/comments]]
 
 By default, anonymous users cannot edit the wiki. This plugin allows
 anonymous web users, who have not signed in, to edit any page in the wiki

doc/plugins/blogspam.mdwn

@@ -1,5 +1,5 @@
 [[!template id=plugin name=blogspam author="[[Joey]]"]]
-[[!tag type/auth]]
+[[!tag type/auth type/comments]]
 
 This plugin adds antispam support to ikiwiki, using the
 [blogspam.net](http://blogspam.net/) API. Both page edits and

doc/plugins/comments.mdwn

@@ -1,5 +1,5 @@
 [[!template id=plugin name=comments author="[[Simon_McVittie|smcv]]"]]
-[[!tag type/web]]
+[[!tag type/web type/comments]]
 
 This plugin adds "blog-style" comments. Unlike the wiki-style freeform 
 Discussion pages, these comments are posted by a simple form, cannot later

doc/plugins/lockedit.mdwn

@@ -1,5 +1,5 @@
 [[!template id=plugin name=lockedit core=1 author="[[Joey]]"]]
-[[!tag type/auth]]
+[[!tag type/auth type/comments]]
 
 This plugin allows the administrator of a wiki to lock some pages, limiting
 who can edit them using the online interface. This doesn't prevent anyone

doc/plugins/moderatedcomments.mdwn

@@ -1,5 +1,5 @@
 [[!template id=plugin name=moderatedcomments author="[[Joey]]"]]
-[[!tag type/auth]]
+[[!tag type/auth type/comments]]
 
 This plugin causes [[comments]] to be held for manual moderation.
 Admins can access the comment moderation queue via their preferences page.

doc/plugins/type/comments.mdwn

@@ -0,0 +1 @@
+These plugins relate to [[plugins/comments]].