Allow std{in,out,err} to be a socket

runtime/bin/file.h

Index: runtime/bin/file.h
diff --git a/runtime/bin/file.h b/runtime/bin/file.h
index 4d9bd4dc5e4341b42a82a3ac83fa4f3cd4ec4756..0fdc398640235f500997b2283d2e12f51313be74 100644
--- a/runtime/bin/file.h
+++ b/runtime/bin/file.h
@@ -46,7 +46,8 @@ class File {
     kTerminal = 0,
     kPipe = 1,
     kFile = 2,
-    kOther = 3
+    kSocket = 3,
+    kOther = -1
   };
 
   enum FileRequest {