gnu: Add linkchecker.

* gnu/packages/web.scm (linkchecker): New variable.

gnu/packages/web.scm

@@ -5054,3 +5054,46 @@ websites lacking feeds.  Supported websites include Facebook, Twitter,
 Instagram and YouTube.")
     (license (list l:public-domain
                    l:expat)))) ;; vendor/simplehtmldom/simple_html_dom.php
+
+(define-public linkchecker
+  (package
+    (name "linkchecker")
+    (version "9.3")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (pypi-uri "LinkChecker" version))
+       (sha256
+        (base32
+         "0v8pavf0bx33xnz1kwflv0r7lxxwj7vg3syxhy2wzza0wh6sc2pf"))))
+    (build-system python-build-system)
+    (inputs
+     `(("python2-requests" ,python2-requests)))
+    (arguments
+     `(#:python ,python-2
+       #:phases
+       (modify-phases %standard-phases
+         ;; Remove faulty python-requests version check. This has been fixed
+         ;; upstream, and can be removed in version 9.4.
+         (add-after 'unpack 'remove-python-requests-version
+           (lambda _
+             (substitute* "linkcheck/__init__.py"
+               (("requests.__version__ <= '2.2.0'") "False"))
+             #t)))))
+    (home-page "https://linkcheck.github.io/linkchecker")
+    (synopsis "Check websites for broken links")
+    (description "LinkChecker is a website validator.  It checks for broken
+links in websites.  It is recursive and multithreaded providing output in
+colored or normal text, HTML, SQL, CSV, XML or as a sitemap graph.  It
+supports checking HTTP/1.1, HTTPS, FTP, mailto, news, nntp, telnet and local
+file links.")
+    (license (list l:gpl2+
+                   l:bsd-2 ; linkcheck/better_exchook2.py
+                   l:bsd-3 ; linkcheck/colorama.py
+                   l:psfl  ; linkcheck/gzip2.py
+                   l:expat ; linkcheck/mem.py
+                   ;; FIXME: Unbundle dnspython and miniboa
+                   ;; This issue has been raised upstream
+                   ;; https://github.com/wummel/linkchecker/issues/729
+                   l:isc   ; third_party/dnspython
+                   l:asl2.0)))) ; third_party/miniboa