Implement several WikiWord handling fixes.

Implement several WikiWord handling fixes.

* lisp/muse-colors.el (muse-link-face): Handle case where no link is
  found by the handlers.  Don't send implicit links through some of the
  advanced checks.

* lisp/muse-mode.el (muse-link-at-point): Move to beginning of first part
  of interwiki link before calling `muse-handle-explicit-link'.

* lisp/muse-wiki.el (muse-wiki-update-interwiki-regexp): Append forgotten
  "\\|" separator between project-alist entries and interwiki entries.
  Force a reconfiguration of muse-colors-markup.

* lisp/muse-wiki.el (muse-wiki-handle-wikiword): Add several checks to be
  sure that we don't colorize WikiNames that don't go with any file.

git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-106