Transition

This PR is simpler than the diff count may suggest.

1. Move consensusSetHash to another file
2. make and make-release now build with the race detector. make xc does not.
3. Siafund diff handling is not on a per-change basis, not a per-block basis (most of the change). This change is non-hardforking.
4. Contracts now pay to the siafund pool immediately, instead of upon expiration (hardforking change).

This hardforking change will not cause any issues until the siafund pool actually has siafunds in it, which it currently does not.