gnu: libxml2: Add search path specification.

* gnu/packages/xml.scm (libxml2)[native-search-paths, search-paths]: New
  fields.
* gnu/packages/gnome.scm (gnome-doc-utils)[arguments]: Remove.
* gnu/packages/gps.scm (gpscorrelate)[arguments]: Remove settings for
  'XML_CATALOG_FILES' from 'configure' phase.
* gnu/packages/web.scm (tinyproxy)[arguments]: Likewise.

gnu/packages/gnome.scm

@@ -143,17 +143,6 @@ The gnome-about program helps find which version of GNOME is installed.")
        (base32
         "19n4x25ndzngaciiyd8dd6s2mf9gv6nv3wv27ggns2smm7zkj1nb"))))
     (build-system gnu-build-system)
-    (arguments
-     `(#:phases
-       (alist-cons-before
-        'check 'pre-check
-        (lambda* (#:key inputs #:allow-other-keys #:rest args)
-          ;; This is needed, because without it, xmlint etc tries
-          ;; to download docbookx.dtd from the net
-          (setenv "XML_CATALOG_FILES" 
-                  (string-append (assoc-ref inputs "docbook-xml") 
-                                 "/xml/dtd/docbook/catalog.xml")))
-        %standard-phases)))
     (native-inputs
      `(("intltool" ,intltool)
        ("docbook-xml" ,docbook-xml-4.4)

gnu/packages/gps.scm

@@ -100,17 +100,7 @@ manipulate maps.")
                      (substitute* "Makefile"
                        (("prefix[[:blank:]]*=.*$")
                         (string-append "prefix = " (assoc-ref outputs "out")
-                                       "\n")))
-
-                     ;; Make sure the DocBook XML and XSL files are found.
-                     ;; Note: this is a space-separated list.
-                     (setenv "XML_CATALOG_FILES"
-                             (string-append (assoc-ref inputs "docbook-xml")
-                                            "/xml/dtd/docbook/catalog.xml "
-                                            (assoc-ref inputs "docbook-xsl")
-                                            "/xml/xsl/"
-                                            ,(package-full-name docbook-xsl)
-                                            "/catalog.xml")))
+                                       "\n"))))
                    %standard-phases)
          #:tests? #f))
       (inputs

gnu/packages/web.scm

@@ -644,16 +644,7 @@ help you implement simple HTTP servers.")
           ;; Uncommenting the next two lines may assist in debugging
           ;; (substitute* "docs/man5/Makefile" (("a2x") "a2x -v"))
           ;; (setenv "XML_DEBUG_CATALOG" "1")
-
-          (setenv "XML_CATALOG_FILES" 
-                  (string-append
-                   (assoc-ref inputs "docbook-xsl") 
-                   "/xml/xsl/docbook-xsl-1.78.1/catalog.xml"
-                   ;; Contrary to the documentation, the file names must
-                   ;; be separated by a space, not a colon.
-                   " " 
-                   (assoc-ref inputs "docbook-xml") 
-                   "/xml/dtd/docbook/catalog.xml")))
+          #t)
         %standard-phases)))
     ;; All of the below are used to generate the documentation
     ;; (Should they be propagated inputs of asciidoc ??)

gnu/packages/xml.scm

@@ -68,6 +68,18 @@ things the parser might find in the XML document (like start tags).")
     (inputs `(("zlib" ,zlib)))
     (native-inputs `(("perl" ,perl)
                      ("python" ,python-2))) ; incompatible with Python 3 (print syntax)
+
+
+    ;; $XML_CATALOG_FILES lists 'catalog.xml' files found in under the 'xml'
+    ;; sub-directory of any given package.
+    (native-search-paths (search-path-specification
+                          (variable "XML_CATALOG_FILES")
+                          (separator " ")
+                          (files '("xml"))
+                          (file-pattern "^catalog\\.xml$")
+                          (file-type 'regular)))
+    (search-paths native-search-paths)
+
     (arguments
      `(#:phases
         (alist-replace