Fix #91: Add support for tty nologin, to start /bin/sh immediately

This patch adds a `nologin` flag to the `tty` configuration directive,
making it possible to set up really simple embedded systems with no
login.

Example, put the following line in `/etc/finit.d/getty.conf` to get
a "Please press Enter to ..." prompt before being presented with a
root shell prompt.

    tty [12345] @console noclear nologin

Needless to say, this is not very secure, but can be really useful
for developer setups, during board bringup, or similar.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/exec.c

@@ -423,6 +423,20 @@ pid_t run_getty2(char *tty, char *cmd, char *args[], int noclear, int nowait, st
 	return pid;
 }
 
+pid_t run_sh(char *tty, int noclear, int nowait, struct rlimit rlimit[])
+{
+	pid_t pid;
+
+	pid = fork();
+	if (!pid) {
+		prepare_tty(tty, B0, "finit-sh", rlimit);
+		if (activate_console(noclear, nowait))
+			_exit(sh(tty));
+	}
+
+	return pid;
+}
+
 int run_parts(char *dir, char *cmd)
 {
 	struct dirent **e;