HELP SYS_UNLOCK_HEAP Revised by Fran Evelyn, July 85
sys_unlock_heap()
SYS_UNLOCK_HEAP reverses the effect of *SYS_LOCK_HEAP; that is, it 'unlocks'
the heap so that the next garbage collection includes the previously locked
area.
See also HELP
*SYS_LOCK_HEAP - locks the heap
*SYSGARBAGE - causes a garbage collection
*POPMEMLIM - on setting the maximum memory size
*POPGCRATIO - helps control determination of memory allocation
*POPMEMUSED - holds total memory used at last garbage collection
*POPGCTIME - holds the CPU time spent on garbage collections