Fix tag-publishing in <insert> and <markup>.

Fix tag-publishing in <insert> and <markup>.

* lisp/muse-publish.el (muse-insert-file-or-string): Don't set
  muse-publish-markup-tags, since that messes other things up for
  <markup> and <insert>.
  (muse-inhibit-style-tags): New variable that specifies whether to
  disable looking for tag definitions that are specific to the current
  style.  This is useful for publishing headers and footers.
  (muse-publish-markup-tag): Use `muse-inhibit-style-tags', but disable
  it unconditionally when calling a tag's function, so that the effect
  does not propagate.

* lisp/muse.el (muse-file-remote-p): New function that detects whether
  the given file path is a remote location.  This is not used yet.
git-archimport-id: mwolson@gnu.org--2006/muse--main--1.0--patch-146