Rename 'dmd' to 'shepherd' in comments and strings.

* build-aux/hydra/demo-os.scm (operating-system)[issue]: Point to
  shepherd instead of dmd.
* ROADMAP: Likewise.
* gnu/build/install.scm (directives): Adjust comment.

ROADMAP

@@ -77,6 +77,6 @@ Freenode!
     + build containers like guix-daemon does
     + provide a Plash-like interface in Bash
   - daemon rewritten in Guile
-  - more dmd integration
+  - more shepherd integration
     + monitor network interfaces and start/stop events based on that
     + include a DHCP client written in Scheme

build-aux/hydra/demo-os.scm

@@ -57,7 +57,7 @@
 
 This image features the GNU Guix package manager, which was used to
 build it (http://www.gnu.org/software/guix/).  The init system is
-GNU dmd (http://www.gnu.org/software/dmd/).
+the GNU Shepherd (http://www.gnu.org/software/shepherd/).
 
 You can log in as 'guest' or 'root' with no password.
 ")

gnu/build/install.scm

@@ -103,7 +103,7 @@ (define (directives store)
     (directory ,store 0 30000 #o1775)
 
     (directory "/etc")
-    (directory "/var/log")                          ; for dmd
+    (directory "/var/log")                          ; for shepherd
     (directory "/var/guix/gcroots")
     (directory "/var/empty")                        ; for no-login accounts
     (directory "/var/db")                           ; for dhclient, etc.