[MINOR] add support for the polling results in fdtab

Now fdtab can contain the FD_POLL_* events so that the pollers
which can fill them can give userful information to readers and
writers about the precise condition of wakeup.
diff --git a/src/checks.c b/src/checks.c
index 0996925..2ae01db 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -336,6 +336,7 @@
 						fdtab[fd].cb[DIR_WR].f = &event_srv_chk_w;
 						fdtab[fd].cb[DIR_WR].b = NULL;
 						fdtab[fd].state = FD_STCONN; /* connection in progress */
+						fdtab[fd].ev = 0;
 						EV_FD_SET(fd, DIR_WR);  /* for connect status */
 #ifdef DEBUG_FULL
 						assert (!EV_FD_ISSET(fd, DIR_RD));