Extend stream functionality

Writer and reader streams now come with methods to write and read
little-endian numbers. Whether that is the right place for such
methods is debatable, but for now, that's where they live.

src/lib/linux_os.rs

@@ -13,6 +13,8 @@ native mod libc = "libc.so.6" {
     fn fclose(FILE f);
     fn fgetc(FILE f) -> int;
     fn ungetc(int c, FILE f);
+    fn fread(vbuf buf, uint size, uint n, FILE f) -> uint;
+    fn fseek(FILE f, int offset, int whence) -> int;
 
     type dir;
     fn opendir(sbuf d) -> dir;