Do not translate the who-prefix or who-suffix if new-style
subsititutions are disabled.
Change memory profile to show the differen between the number of
objects at each call.
Bound the layout cache size.

This helps ensure that code that creates many text objects in a
single interaction will now consume unbounded memory if it lets
those Text objects be GCed.
Prevent memory leaks via the rollback log.

Before this change, code that created and then immediately modified a
list, dict, set, or object that was rollback-able would cause a small
memory leak until the end of the interaction.