C++: Fix build using Clang 3.1

Build of the arakoonmm C++ bindings failed using Clang 3.1. This commit
fixes the build.

Thanks to Bastiaan Stougie <bastiaan.stougie@amplidata.com> for
providing the necessary pointer (pun intended).

Change-Id: If804b65ab26c12d538ae03163aee953779434dfa
Closes: #8
See: https://github.com/Incubaid/crakoon/issues/8