kqueue and epoll code wasn't checking for EINTR properly, leading to hangs

basis/io/unix/backend/backend.factor

@@ -207,10 +207,10 @@ TUPLE: mx-port < port mx ;
 : <mx-port> ( mx -- port )
     dup fd>> mx-port <port> swap >>mx ;
 
-: multiplexer-error ( n -- )
-    0 < [
+: multiplexer-error ( n -- n )
+    dup 0 < [
         err_no [ EAGAIN = ] [ EINTR = ] bi or
-        [ (io-error) ] unless
+        [ drop 0 ] [ (io-error) ] if
     ] when ;
 
 : ?flag ( n mask symbol -- n )

basis/io/unix/epoll/epoll.factor

@@ -49,7 +49,7 @@ M: epoll-mx remove-output-callbacks ( fd mx -- seq )
 
 : wait-event ( mx us -- n )
     [ [ fd>> ] [ events>> ] bi [ underlying>> ] [ length ] bi ] [ 1000 /i ] bi*
-    epoll_wait dup multiplexer-error ;
+    epoll_wait multiplexer-error ;
 
 : handle-event ( event mx -- )
     [ epoll-event-fd ] dip

basis/io/unix/kqueue/kqueue.factor

@@ -58,8 +58,7 @@ M: kqueue-mx remove-output-callbacks ( fd mx -- seq )
     [
         [ fd>> f 0 ]
         [ events>> [ underlying>> ] [ length ] bi ] bi
-    ] dip kevent
-    dup multiplexer-error ;
+    ] dip kevent multiplexer-error ;
 
 : handle-kevent ( mx kevent -- )
     [ kevent-ident swap ] [ kevent-filter ] bi {