gnu: Rename module mailutils to mail.

* gnu/packages/mail.scm: Rename from gnu/packages/mailutils.scm.
* gnu-system.am: Rename the module.

gnu-system.am

@@ -115,7 +115,7 @@ GNU_SYSTEM_MODULES =				\
   gnu/packages/lua.scm				\
   gnu/packages/lvm.scm				\
   gnu/packages/m4.scm				\
-  gnu/packages/mailutils.scm			\
+  gnu/packages/mail.scm				\
   gnu/packages/make-bootstrap.scm		\
   gnu/packages/maths.scm			\
   gnu/packages/mit-krb5.scm			\

gnu/packages/mail.scm

@@ -16,7 +16,7 @@
 ;;; You should have received a copy of the GNU General Public License
 ;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
 
-(define-module (gnu packages mailutils)
+(define-module (gnu packages mail)
   #:use-module (gnu packages)
   #:use-module (gnu packages linux)
   #:use-module (gnu packages gnutls)