gnu: emacs-w3m: Update and allow builds with Emacs 26.

* gnu/packages/emacs.scm (emacs-w3m)[source]: Grab the source from
github.com.
[native-inputs]: Add TEXINFO.
[arguments]: Add 'support-emacs!' phase.  In 'patch-exec-paths' phase,
make w3m.el and w3m-image.el writable.  Remove substitution for
'w3m-image-viewer', which no longer exists.

gnu/packages/emacs.scm

@@ -748,18 +748,24 @@ provides an optional IDE-like error list.")
 ;;;
 
 (define-public emacs-w3m
+  ;; Emacs-w3m follows a "rolling release" model from its CVS repo.  We could
+  ;; use CVS, sure, but instead we choose to use this Git mirror described on
+  ;; the home page as an "unofficial" mirror.
+  (let ((commit "0dd5691f46d314a84da63f3a7277d721815811a2"))
     (package
       (name "emacs-w3m")
-    (version "1.4.538+0.20141022")
+      (version (git-version "1.5" "0" commit))
       (source (origin
-             (method url-fetch)
+                (method git-fetch)
-             (uri (string-append "mirror://debian/pool/main/w/w3m-el/w3m-el_"
+                (uri (git-reference
-                                 version ".orig.tar.gz"))
+                      (url "https://github.com/ecbrown/emacs-w3m")
+                      (commit commit)))
                 (sha256
                  (base32
-               "0zfxmq86pwk64yv0426gnjrvhjrgrjqn08sdcdhmmjmfpmqvm79y"))))
+                  "02xalyxbrkgl4n8nj7xxkmsbm6lshhwdc8bzs2l4wz3hkpgkj7x4"))))
       (build-system gnu-build-system)
       (native-inputs `(("autoconf" ,autoconf)
+                       ("texinfo" ,texinfo)
                        ("emacs" ,emacs-minimal)))
       (inputs `(("w3m" ,w3m)
                 ("imagemagick" ,imagemagick)))
@@ -785,20 +791,28 @@ provides an optional IDE-like error list.")
            (add-after 'unpack 'autoconf
              (lambda _
                (zero? (system* "autoconf"))))
+           (add-before 'configure 'support-emacs!
+             (lambda _
+               ;; For some reason 'AC_PATH_EMACS' thinks that 'Emacs 26' is
+               ;; unsupported.
+               (substitute* "configure"
+                 (("EMACS_FLAVOR=unsupported")
+                  "EMACS_FLAVOR=emacs"))
+               #t))
            (add-before 'build 'patch-exec-paths
              (lambda* (#:key inputs outputs #:allow-other-keys)
                (let ((out (assoc-ref outputs "out"))
                      (w3m (assoc-ref inputs "w3m"))
                      (imagemagick (assoc-ref inputs "imagemagick"))
                      (coreutils (assoc-ref inputs "coreutils")))
+                 (make-file-writable "w3m.el")
                  (emacs-substitute-variables "w3m.el"
                    ("w3m-command" (string-append w3m "/bin/w3m"))
                    ("w3m-touch-command"
                     (string-append coreutils "/bin/touch"))
-                 ("w3m-image-viewer"
-                  (string-append imagemagick "/bin/display"))
                    ("w3m-icon-directory"
                     (string-append out "/share/images/emacs-w3m")))
+                 (make-file-writable "w3m-image.el")
                  (emacs-substitute-variables "w3m-image.el"
                    ("w3m-imagick-convert-program"
                     (string-append imagemagick "/bin/convert"))
@@ -818,7 +832,7 @@ provides an optional IDE-like error list.")
       (synopsis "Simple Web browser for Emacs based on w3m")
       (description
        "Emacs-w3m is an emacs interface for the w3m web browser.")
-    (license license:gpl2+)))
+      (license license:gpl2+))))
 
 (define-public emacs-wget
   (package