Port Shea Levy's socket activation patch to version 2.1.1.

diff -Naur gnupg-2.1.1-upstream/agent/gpg-agent.c gnupg-2.1.1/agent/gpg-agent.c
--- gnupg-2.1.1-upstream/agent/gpg-agent.c	2014-12-01 05:04:57.000000000 -0430
+++ gnupg-2.1.1/agent/gpg-agent.c	2014-12-23 17:13:48.029286035 -0430
@@ -125,7 +125,9 @@
   oPuttySupport,
   oDisableScdaemon,
   oDisableCheckOwnSocket,
-  oWriteEnvFile
+  oWriteEnvFile,
+  oAgentFD,
+  oSSHAgentFD
 };
 
 
@@ -143,6 +145,8 @@
   ARGPARSE_group (301, N_("@Options:\n ")),
 
   ARGPARSE_s_n (oDaemon,  "daemon", N_("run in daemon mode (background)")),
+  ARGPARSE_s_i (oAgentFD,  "agent-fd", "@"),
+  ARGPARSE_s_i (oSSHAgentFD,  "ssh-agent-fd", "@"),
   ARGPARSE_s_n (oServer,  "server", N_("run in server mode (foreground)")),
   ARGPARSE_s_n (oVerbose, "verbose", N_("verbose")),
   ARGPARSE_s_n (oQuiet,	  "quiet",     N_("be somewhat more quiet")),
@@ -627,6 +631,31 @@
   return 1; /* handled */
 }
 
+/* Handle agent socket(s) */
+static void
+handle_agent_socks(int fd, int fd_extra, int fd_ssh)
+{
+#ifndef HAVE_W32_SYSTEM
+  if (chdir("/"))
+    {
+      log_error ("chdir to / failed: %s\n", strerror (errno));
+      exit (1);
+    }
+
+  {
+    struct sigaction sa;
+
+    sa.sa_handler = SIG_IGN;
+    sigemptyset (&sa.sa_mask);
+    sa.sa_flags = 0;
+    sigaction (SIGPIPE, &sa, NULL);
+  }
+#endif /*!HAVE_W32_SYSTEM*/
+
+  log_info ("%s %s started\n", strusage(11), strusage(13) );
+  handle_connections (fd, fd_extra, fd_ssh);
+  assuan_sock_close (fd);
+}
 
 /* The main entry point.  */
 int
@@ -643,6 +672,8 @@
   int default_config =1;
   int pipe_server = 0;
   int is_daemon = 0;
+  int fd_agent = GNUPG_INVALID_FD;
+  int fd_ssh_agent = GNUPG_INVALID_FD;
   int nodetach = 0;
   int csh_style = 0;
   char *logfile = NULL;
@@ -850,6 +881,8 @@
         case oSh: csh_style = 0; break;
         case oServer: pipe_server = 1; break;
         case oDaemon: is_daemon = 1; break;
+        case oAgentFD: fd_agent = pargs.r.ret_int; break;
+        case oSSHAgentFD: fd_ssh_agent = pargs.r.ret_int; break;
 
         case oDisplay: default_display = xstrdup (pargs.r.ret_str); break;
         case oTTYname: default_ttyname = xstrdup (pargs.r.ret_str); break;
@@ -940,7 +973,8 @@
     bind_textdomain_codeset (PACKAGE_GT, "UTF-8");
 #endif
 
-  if (!pipe_server && !is_daemon && !gpgconf_list)
+  if (!pipe_server && !is_daemon && !gpgconf_list &&
+                                                  fd_agent == GNUPG_INVALID_FD)
     {
      /* We have been called without any options and thus we merely
         check whether an agent is already running.  We do this right
@@ -1090,6 +1124,10 @@
       agent_deinit_default_ctrl (ctrl);
       xfree (ctrl);
     }
+  else if (fd_agent != GNUPG_INVALID_FD)
+    {
+      handle_agent_socks(fd_agent, GNUPG_INVALID_FD, fd_ssh_agent);
+    }
   else if (!is_daemon)
     ; /* NOTREACHED */
   else
@@ -1287,26 +1325,8 @@
           log_set_prefix (NULL, oldflags | JNLIB_LOG_RUN_DETACHED);
           opt.running_detached = 1;
         }
-
-      if (chdir("/"))
-        {
-          log_error ("chdir to / failed: %s\n", strerror (errno));
-          exit (1);
-        }
-
-      {
-        struct sigaction sa;
-
-        sa.sa_handler = SIG_IGN;
-        sigemptyset (&sa.sa_mask);
-        sa.sa_flags = 0;
-        sigaction (SIGPIPE, &sa, NULL);
-      }
-#endif /*!HAVE_W32_SYSTEM*/
-
-      log_info ("%s %s started\n", strusage(11), strusage(13) );
-      handle_connections (fd, fd_extra, fd_ssh);
-      assuan_sock_close (fd);
+#endif /*!HAVE_W32_SYSTEM*/      
+      handle_agent_socks(fd, fd_extra, fd_ssh);
     }
 
   return 0;
diff -Naur gnupg-2.1.1-upstream/doc/gpg-agent.texi gnupg-2.1.1/doc/gpg-agent.texi
--- gnupg-2.1.1-upstream/doc/gpg-agent.texi	2014-12-05 09:56:37.000000000 -0430
+++ gnupg-2.1.1/doc/gpg-agent.texi	2014-12-23 16:26:38.366391186 -0430
@@ -43,7 +43,15 @@
 .IR file ]
 .RI [ options ]
 .B  \-\-daemon
-.RI [ command_line ]
+.br
+.B  gpg-agent
+.RB [ \-\-homedir
+.IR dir ]
+.RB [ \-\-options
+.IR file ]
+.RI [ options ]
+.B  \-\-agent-fd
+.IR fd
 @end ifset
 
 @mansect description
@@ -186,6 +194,11 @@
 a new process as a child of gpg-agent: @code{gpg-agent --daemon
 /bin/sh}.  This way you get a new shell with the environment setup
 properly; if you exit from this shell, gpg-agent terminates as well.
+
+@item --agent-fd @var{fd}
+@opindex  agent-fd
+Start the gpg-agent using @var{fd} as the listening socket. This is useful for
+socket activation a la systemd and launchd.
 @end table
 
 @mansect options
@@ -545,6 +558,12 @@
 remote machine.
 
 
+@item --ssh-agent-fd @var{fd}
+@opindex ssh-agent-fd
+
+When starting the agent with @option{--agent-fd}, use this to pass in a socket
+to be used for the OpenSSH agent protocol.
+
 @anchor{option --enable-ssh-support}
 @item --enable-ssh-support
 @opindex enable-ssh-support