memory_summary - return a summary of memory usage

mapping memory_summary();

memory_summary() returns a mapping of the form:

PRE( ([ program name : ([ var name : mem usage, ... ]) ... ]) )

the memory usage is the memory required to store the value divided by the number of variables pointing to that particular value. [Due to sharing of values, giving an exact number for the memory usage of any value is impossible]

This efun is only available if PACKAGE_CONTRIB is defined.