ChangeLog: add cf-promises note about --eval-functions and new behavior
Cache result of some functions.

This adds the boolean constraint 'cache_system_functions' to
common control, defaulting to true. Functions classified as such
will be memoized for the duration of an agent run.
Redmine#3283: add a check for non-matching query
Redmine#3283: StringSetFromString handles NULL strings.  New StringSetToBuffer function.
Redmine#3283: Add tags string parameter to all the class and variable creating functions.
Redmine#3283: Fix search logic in variablesmatching and classesmatching.
Redmine#3283: add a check for non-matching classesmatching query
Redmine#3283: tag all classes and variables created by all agents