Fix sudoedit when running with SELinux RBAC mode.

We can't use run_command() to run sesh, that will use the sudo event
loop (and might run it in a pty!).
There's no need to relabel the tty when copying files.
Get the path to sesh from sudo.conf.

Currently, for SELinux RBAC, the editor runs with the target user's
security context. This defeats the purpose of sudoedit.  Fixing
that requires passing file descriptors between the main sudo process
(running with the invoking user's security context) and sesh (runnning
with the target user's security context).

src/sudo.c

@@ -974,10 +974,6 @@ run_command(struct command_details *details)
     case CMD_WSTATUS:
 	/* Command ran, exited or was killed. */
 	status = cstat.val;
-#ifdef HAVE_SELINUX
-	if (ISSET(details->flags, CD_SUDOEDIT_COPY))
-	    break;
-#endif
 	iolog_close(status, 0);
 	policy_close(status, 0);
 	audit_close(SUDO_PLUGIN_WAIT_STATUS, cstat.val);