Fix ae.c to avoid timers infinite loop.

This fix was suggested by Anthony LaTorre, that provided also a good
test case that was used to verify the fix.

The problem with the old implementation is that, the time returned by
a timer event (that is the time after it want to run again) is added
to the event *start time*. So if the event takes, in order to run, more
than the time it says it want to be scheduled again for running, an
infinite loop is triggered.

src/anet.h

@@ -31,6 +31,8 @@
 #ifndef ANET_H
 #define ANET_H
 
+#include <sys/types.h>
+
 #define ANET_OK 0
 #define ANET_ERR -1
 #define ANET_ERR_LEN 256