query_time_mode and other vars on session, force join+subquery+count to be simulated with select
deny write in time-query mode
refactor fieldmap operations into Select, should no longer be any cases where $select->run is called directly in query_time_mode
first bits toward the query module
basic point-in-time query tests
relational point-in-time tests
make query_start_time and query_end_time functional
implement primitive query cache for historical mode.  will need to remeasure this in real-world setting to confirm win
time breakpoint collection
query_point_in_time/query_history driver functions