bug#11839: teach some url code about .xz files

[Liam Stitt]

Hi.  The code in lisp/url knows about .gz and .bz2 files, but not about the
more recent .xz variety.  These two trivial patches correct this:

*** url-file.el~        2012-01-16 02:12:46.000000000 -0700
--- url-file.el 2012-07-01 20:26:10.000000000 -0600
*************** can do automatic decompression for them,
*** 41,47 ****
  'foo.gz' exists, even though the FTP server would happily serve it up
  to them."
    (let ((scratch nil)
!       (compressed-extensions '("" ".gz" ".z" ".Z" ".bz2"))
        (found nil))
      (while (and compressed-extensions (not found))
        (if (file-exists-p (setq scratch (concat fname (pop 
compressed-extensions))))
--- 41,47 ----
  'foo.gz' exists, even though the FTP server would happily serve it up
  to them."
    (let ((scratch nil)
!       (compressed-extensions '("" ".gz" ".z" ".Z" ".bz2" ".xz"))
        (found nil))
      (while (and compressed-extensions (not found))
        (if (file-exists-p (setq scratch (concat fname (pop 
compressed-extensions))))
*************** to them."
*** 178,183 ****
--- 178,184 ----
                             (\.uue "x-uuencoded")
                             (\.hqx "x-hqx")
                             (\.bz2 "x-bzip2")
+                            (\.xz "x-xz")
                             (otherwise nil)))
  
      (if (file-directory-p filename)

*** url-vars.el~        2012-07-01 19:48:37.000000000 -0600
--- url-vars.el 2012-07-01 20:25:46.000000000 -0600
*************** variable."
*** 152,158 ****
                                    (".uue" . "x-uuencoded")
                                    (".hqx" . "x-hqx")
                                    (".Z"  . "x-compress")
!                                   (".bz2"  . "x-bzip2"))
    "An alist of file extensions and appropriate content-transfer-encodings."
    :type '(repeat (cons :format "%v"
                       (string :tag "Extension")
--- 152,159 ----
                                    (".uue" . "x-uuencoded")
                                    (".hqx" . "x-hqx")
                                    (".Z"  . "x-compress")
!                                   (".bz2"  . "x-bzip2")
!                                   (".xz"  . "x-xz"))
    "An alist of file extensions and appropriate content-transfer-encodings."
    :type '(repeat (cons :format "%v"
                       (string :tag "Extension")