Make customize of muse-project-alist work in Emacs21 and XEmacs.

Make customize of muse-project-alist work in Emacs21 and XEmacs.

* lisp/muse.el (muse-widget-type-value-create)
  (muse-widget-child-value-get, muse-widget-type-match): Minimum set of
  extra widgets from 'lazy type that are needed to get the
  `muse-project-alist' customize interface to work on XEmacs and Emacs21.

* lisp/muse.el (muse-implicit-link-functions)
  (muse-explicit-link-functions): Remove predefined wiki-related options.
  These are added in muse-wiki via custom-add-option.

* lisp/muse-mode.el (muse-mode-hook): Ditto.

* lisp/muse-colors.el (muse-colors-emphasized): Use eq instead of memq.

* lisp/muse-project.el (muse-project-alist-get): Turn :symbols into
  ":strings" to cope with Emacs21 and XEmacs.
  (muse-project-alist-set): Turn ":strings" back into ":symbols".

* lisp/muse-project.el (muse-project): Derive from 'default rather than
  'lazy, since that is an Emacs CVS-ism.  Separate logical groups with
  newlines.  Control indentation.  Remove an unnecessary inlined repeat.

* lisp/muse-project.el (muse-project-alist): Use cons instead of alist,
  since XEmacs doesn't support the alist widget.  Deal with case where no
  projects are defined, or a strange expression is used.

* lisp/muse-wiki.el: Insinuate muse-wiki link handlers and mode hook
  stuff using custom-add-option.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-155