subredditInfo hover in comments

Change to href to avoid instances in comments where the user creates a
link with a different name than the target subreddit, eg [RES
issues](/r/RESissues), instead of just /r/RESissues.

Also strips the trailing slash so that cached subreddit names are always
SR_NAME and not SR_NAME/
Stop thumbnails being assigned href of image links

Any text post expando that contains an image will then cause that post's
thumbnail to inherit its href.
Merge pull request #587 from gavin19/master

subredditInfo hover in comments