Add dependencies to benchmarks project in "core" solution.
Add dependencies to benchmarks project in "core" solution.

These aren't picked up automatically due to the way we pull in the dependencies in the benchmarks project file itself, allowing the multi-version benchmarking.

jskeet/nodatime,malcolmr/nodatime,nodatime/nodatime,BenJenkinson/nodatime,malcolmr/nodatime,BenJenkinson/nodatime,nodatime/nodatime,malcolmr/nodatime,jskeet/nodatime,malcolmr/nodatime