parlib: Use a relative timer for abort_sysc

The issue is that the timer goes off before the syscall could block.  If
the timer was very far in the past, such as due to a go test that put the
alarm 30 seconds in the past, we would do N loops, each of which fires
instantly, until we finally set an alarm for the future.

Using a relative timer fixes that.  Also, one second is a bit much - enough
that an interactive user might notice and wonder if something is broken.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>

user/parlib/alarm.c

diff --git a/user/parlib/alarm.c b/user/parlib/alarm.c
index 4878bf4..0e1b336 100644
--- a/user/parlib/alarm.c
+++ b/user/parlib/alarm.c
@@ -478,7 +478,7 @@
 		 * unblocking, or even has returned, but hasn't cancelled the alarm.
 		 * regardless, we request a new alarm (the uthread will cancel us one
 		 * way or another). */
-		set_awaiter_inc(awaiter, 1000000);
+		set_awaiter_rel(awaiter, 10000);
 		__set_alarm(awaiter);
 		return;
 	}