Switch some functions to return bool, and change would_need_scratch to need_scratch_setup and make it bool.
Introduce Switchable enum and use it for function return values and for Task::switchable.
Fix some return types for util.h functions.
Switch some variables from int to bool.
Make Task::unstable a bool.
Switch more Task fields to bool.
Trivial fix for return value from boolean function
Fix function return types in record_signal.cc.