gnu: texlive-bin: Fix the tlmgr utility.

Previously, it would error out, not finding its Perl modules, and later not
finding config.guess.  This utility is useful to query the local TeX Live
package database (texlive.tlpdb).

(texlive-bin)[inputs]{config}: New input.
[phases]{postint}: Add a symlink to the 'config.guess' script.  Patch the
tlmgr.pl script so that it can find its Perl modules and other resources.

gnu/packages/tex.scm

@@ -279,6 +279,7 @@ (define-public texlive-bin
     (build-system gnu-build-system)
     (inputs
      `(("texlive-extra-src" ,texlive-extra-src)
+       ("config" ,config)
        ("texlive-scripts"
         ,(origin
            (method svn-fetch)
@@ -452,6 +453,16 @@ (define-public texlive-bin
                  (("\\$TEXMFROOT/")
                   (string-append share "/")))
 
+               ;; Likewise for the tlmgr.
+               (substitute* (string-append scripts "/tlmgr.pl")
+                 ((".*\\$::installerdir = \\$Master.*" all)
+                  (format #f "  $Master = ~s;~%~a" share all)))
+
+               ;; Install the config.guess script, required by tlmgr.
+               (with-directory-excursion share
+                 (mkdir-p "tlpkg/installer/")
+                 (symlink config.guess "tlpkg/installer/config.guess"))
+
                ;; texlua shebangs are not patched by the patch-source-shebangs
                ;; phase because the texlua executable does not exist at that
                ;; time.