io.backend: start signal thread after io-backend

The c-io-backend can't handle input-ports and raises an error during bootstrap.

basis/io/backend/unix/linux/linux.factor

@@ -2,10 +2,12 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: kernel system namespaces io.files.unix io.backend
 io.backend.unix io.backend.unix.multiplexers
-io.backend.unix.multiplexers.epoll ;
+io.backend.unix.multiplexers.epoll init ;
 IN: io.backend.unix.linux
 
 M: linux init-io ( -- )
     <epoll-mx> mx set-global ;
 
 linux set-io-backend
+
+[ start-signal-pipe-thread ] "io.backend.unix:signal-pipe-thread" add-startup-hook

basis/io/backend/unix/macosx/macosx.factor

@@ -3,7 +3,7 @@
 USING: io.backend system namespaces
 io.backend.unix.multiplexers io.backend.unix.multiplexers.run-loop
 kernel accessors assocs continuations unix io.backend.unix
-io.backend.unix.multiplexers.kqueue io.files.unix ;
+io.backend.unix.multiplexers.kqueue io.files.unix init ;
 IN: io.backend.unix.macosx
 
 SINGLETON: macosx-kqueue
@@ -15,3 +15,5 @@ M: macosx init-io ( -- )
     <run-loop-mx> mx set-global ;
 
 macosx set-io-backend
+
+[ start-signal-pipe-thread ] "io.backend.unix:signal-pipe-thread" add-startup-hook

basis/io/backend/unix/unix.factor

@@ -7,7 +7,7 @@ io.encodings math.parser continuations system libc namespaces
 make io.timeouts io.encodings.utf8 destructors
 destructors.private accessors summary combinators locals
 unix.time unix.types fry io.backend.unix.multiplexers
-classes.struct init ;
+classes.struct ;
 QUALIFIED: io
 IN: io.backend.unix
 
@@ -226,5 +226,3 @@ TUPLE: mx-port < port mx ;
 
 :: ?flag ( n mask symbol -- n )
     n mask bitand 0 > [ symbol , ] when n ;
-
-[ start-signal-pipe-thread ] "io.backend.unix:signal-pipe-thread" add-startup-hook