Fix pass-by-reference in bulirsch_stoer_dense_out
bulirsch_stoer_dense_out always passed the ODE system as value to its underlying midpoint method.
Merge pull request #129 from wschreyer/master

Fix pass-by-reference in bulirsch_stoer_dense_out.
 exceptions are handled by BOOST_THROW_EXCEPTION so that the compiler option fno-exceptions can be used without errors