gnu: libgcrypt: Replace with 1.7.3 [fixes CVE-2016-6316].

* gnu/packages/gnupg.scm (libgcrypt)[replacement]: New field.
(libgcrypt-1.7.3): New variable.

gnu/packages/gnupg.scm

@@ -74,6 +74,7 @@ (define-public libgpg-error
 (define-public libgcrypt
   (package
     (name "libgcrypt")
+    (replacement libgcrypt-1.7.3)
     (version "1.7.0")
     (source (origin
              (method url-fetch)
@@ -107,6 +108,19 @@ (define-public libgcrypt
     (properties '((ftp-server . "ftp.gnupg.org")
                   (ftp-directory . "/gcrypt/libgcrypt")))))
 
+(define-public libgcrypt-1.7.3
+  (package
+    (inherit libgcrypt)
+    (source
+     (let ((version "1.7.3"))
+       (origin
+         (method url-fetch)
+         (uri (string-append "mirror://gnupg/libgcrypt/libgcrypt-"
+                             version ".tar.bz2"))
+         (sha256
+          (base32
+           "0wbh6fq5zi9wg2xcfvfpwh7dv52jihivx1vm4h91c2kx0w8n3b6x")))))))
+
 (define-public libgcrypt-1.5
   (package (inherit libgcrypt)
     (replacement libgcrypt-1.5.6)