They take a pointer to a free-list used for hashlinks so the hashlink
pools can be per-thread. However, hash tables that are not updated are
always thread-safe, so this affects only updates. progs_t has been set
up such that it is easy for multiple progs within one thread can share
hashlinks.
This is an extension "wrapper" (no such C function). This allows ruamoko
programs to read property lists without worrying about the memory required
to store the string for the property list being read.
The plist code was written long before I thought of resource handles, and
then it was forgotten. This is much nicer and safer than storing C
pointers in progs memory space (*shudder*).
