This commit brings a new implementation for HARDMEMTESTS, which forces
an emergency GC whenever possible. It also fixes some issues detected
with this option:
- A small bug in lvm.c: a closure could be collected by an emergency
GC while being initialized.
- Some tests: a memory address can be immediatly reused after a GC;
for instance, two consecutive '{}' expressions can return exactly the
same address, if the first one is not anchored.
d36a31e673