fix mmap_shared

CHANGES

@@ -6,6 +6,7 @@
     ' '; needed for web servers, so they can serve libstdc++.tar.gz)
   fix iob_write to handle failure properly
   document that the iob_write callback should limit itself
+  fix mmap_shared
   add iob_free, add man pages for iob_free and iob_reset
 
 0.21:

mmap/mmap_shared.c

@@ -23,7 +23,7 @@ extern char* mmap_shared(const char* filename,unsigned long* filesize) {
   CloseHandle(fd);
   return map;
 #else
-  int fd=open_read(filename);
+  int fd=open_rw(filename);
   char *map;
   if (fd>=0) {
     *filesize=lseek(fd,0,SEEK_END);