XEmacs fixes in muse-latex2png and muse-registry.

XEmacs fixes in muse-latex2png and muse-registry.

* lisp/muse-latex2png.el (latex2png): Fix XEmacs error.  It seems better
  to use expand-file-name than concat, since the result of the
  temp-directory function sometimes doesn't have a trailing backslash.

* lisp/muse-registry.el (muse-registry-url-regexp): Use
  muse-regexp-space.
  (muse-registry-get-project-name): Use muse-replace-regexp-in-string.
  (muse-registry-make-new-registry): Use a better heuristic for
  determining whether the given file is actually a directory.  This
  avoids the use of `directory-files-and-attributes', which is not
  available in XEmacs.
  (muse-registry-new-entries): Use muse-match-string-no-properties.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-288