Memory pool: Add ASAN poisoning/unpoisoning
Memory pool: Add ASAN poisoning/unpoisoning

Add ASAN poisoning/unpoisoning to the POOL FREE code (not in use yet).
The idea is to mark freed pool elements so an ASAN error will occur if
they are accessed. When such elements are reallocate, this mark is
removed.

These macros are no-op if not compiled with ASAN.

ampli/link-grammar,opencog/link-grammar,opencog/link-grammar,opencog/link-grammar,ampli/link-grammar,opencog/link-grammar,linas/link-grammar,opencog/link-grammar,ampli/link-grammar,linas/link-grammar,linas/link-grammar,opencog/link-grammar,linas/link-grammar,opencog/link-grammar,ampli/link-grammar,linas/link-grammar,ampli/link-grammar,ampli/link-grammar,ampli/link-grammar,ampli/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar,linas/link-grammar,opencog/link-grammar