#18 Enable use of std::tr1::shared_ptr on C++ TR1 compilers

[Raspy]

Since the only feature being used from boost seems to be shared_ptr, it could be enabled to use std::tr1::shared_ptr instead on compilers that support C++ TR1 standard. Configure could check for tr1/memory header before boost/share_ptr.hpp. This would enable compiling software on a decent compiler (e.g. gcc >= 4.1) without requiring boost. Of course it could always fallback to boost if tr1/memory is not available.

[Scott Finneran]

Replaced the boost shared_ptr and static_assert implementations with std.