#14 Compiler errror

[Jonas Gehring]

The current version (0.85) doesn't compile on my Arch Linux box (gcc (GCC) 4.6.1 20110819 (prerelease)):

tree.h:118:21: error: 'ptrdiff_t' does not name a type

Including cstddef in tree.h fixes this problem.

- Jonas

[Alex]

Fix: Include cstddef in the header "tree.h"
#include <cstddef>