Add configuration to restrict the formats allowed for comments

I want to write my blog posts in a convenient format (Emacs org mode)
but do not want commenters to be able to use this format for security
reasons. This patch allows to configure which formats are allowed for
writing comments.

Effectively, it restricts the formats enabled with add_plugin to those
mentioned in comments_allowformats. If this is empty, all formats are
allowed, which is the behavior without this patch.
page.tmpl: omit searchform, trails, sidebar and most metadata in CGI

These all seem somewhat inappropriate (searchform and sidebar are
arguable either way). I've left actions and languages enabled, since
they seem more reasonable for CGI-generated pages.

Bug: http://ikiwiki.info/bugs/trail_shows_on_cgi_pages/
Signed-off-by: Simon McVittie <smcv@debian.org>
Revert spam

This reverts commit a867da05bbdd0ee8765de21db27aebfe3d9fc0e5.
Revert spam

This reverts commit 871545c27c7e477c26b008434de216be44c585bd.
Revert spam

This reverts commit 3281e185ee8ce13348e7cf4fb3b14837af651197.
theme: Now <TMPL_IF THEME_$NAME> can be used in all templates when a theme is enabled.
Revert 2 spam commits
new topic re 2rand[0,1,1] spam
Added a comment
Added a comment
Added a comment: SOLVED -- How can I prevent spam?
notifyemail: Fix bug that caused duplicate emails to be sent when site was rebuilt.
Merge branch 'master' of ssh://git.ikiwiki.info
bzr: bzr rm no longer has a --force option, remove
releasing version 3.20130518