admin/feedback: make sure that "Mark checked item as (Ham|Spam)" do what they say.

The behaviour of these was to just toggle the state, now they are
actually marking them as ham/spam so that they don't misbehave.
akismet: save the user agent and submit it when checking for/submitting spam.

The User-Agent sent by the commenter is often a good piece of
information to identify whether a comment is spam or not, so make sure
not to blackhole it and instead store and submit it.
Update schema
gravatar: use protocol-relative URIs for HTTPS compatibility.
comments: use relative URLs for comment forms.

Using full, absoltue URLs will cause testing environment to comment on
production instances, and will also break HTTPS support on
mixed-protocols sites.
Fix specs
Remove executable permissions to files that shouldn't be executed.
Fix links to relative paths instead of absolute paths.

This unbreaks the view on a local test system and supports HTTPS more
properly.
excerpts: pre-process the excerpts with the filter

This allows posts with markup early in the body to not show said markup.
Remove now-useless failing spec
Add very basic support for OpenGraph data.

This allows at least the title of the page and the title of the site
to be expressed as OpenGraphs
Fix usage of undefined "article" variable.
Avoid using capturing regexps just to make sure that substitutions will happen.
Avoid resetting tags when posts are published via trigger.
Merge branch 'several-fixes'

Merges in most of pull request #145.