Put Silotree files in O.silotree.
Remove txn_proto1.
is_read_only() becomes is_snapshot().

Better name, agrees with paper.
Internal: Change consistent_snapshot_tid() interface

In many places the snapshot_tid() was only used in verbosery.
Don't save it on the stack for that. And just return the tid itself.
Choose commit epoch at the commit point.
Merge pull request #10 from kohler/master

choose epoch right