Fix build failure when compiling with -D_FORTIFY_SOURCE=2

See http://www.opencascade.org/org/forum/thread_14325/
Patch written by Andrea Florio for openSUSE.

Index: opencascade/ros/src/WOKUnix/WOKUnix_FDescr.cxx
===================================================================
--- opencascade.orig/ros/src/WOKUnix/WOKUnix_FDescr.cxx
+++ opencascade/ros/src/WOKUnix/WOKUnix_FDescr.cxx
@@ -202,7 +202,7 @@
   if(mknod(apath.ToCString(), 0700 |  S_IFIFO, 0)) 
     { perror(apath.ToCString());}
 
-  myFileChannel = open(apath.ToCString(),  O_RDONLY | O_NDELAY | O_CREAT);
+  myFileChannel = open(apath.ToCString(), O_RDONLY | O_NDELAY | O_CREAT, S_IRUSR);
   SetUnBuffered();
 
   // write end of pipe is unbuffered also 
