edit-server.el: avoid redundant call to hooks (#92)

If we don't clear the kill-buffer-hook we'll end up doing it all over
again!
testareas.js: make it more obvious when hiding textareas (#93)

This is not a fix but will make it obvious in the console log when we
have hidden a text area. Unfortunately when the Blogger text area
comes into focus it doesn't seem to trigger a DOM update.

Maybe we should just skip adding buttons but still allow event mapping.
edit-server.el: do not call `set-buffer-multibyte` in the process buffer

In edit-server-accept, set-buffer-multibyte is called, but it's applied to
whatever buffer was previously active because the call is not wrapped with
`with-current-buffer`. This makes edit-server fail if that previously
active buffer is an indirect buffer (set-buffer-multibyte is illegal in an
indirect buffer).

Rather than add with-current-buffer, though, just remove the call
altogether. It is not necessary for the process buffer to be multibyte.
Merge pull request #95 from dato/indirect-buffer-fix