{
{  The purpose of this procedure is to search through the free blocks in a heap,
{and free pages entirely contained within the blocks.
{  The heap descriptor for each block must remain in memory.  The first two
{words of each block contain the heap descriptor.  The heap descriptor will
{always begin on a (16 MOD 32) boundary.  This eliminates the need to
{specially consider end cases.
{  MMP$FREE_PAGES frees only pages entirely contained within the block.
{Therefore, the beginning pva or length of the block neednt be adjusted
{to page boundaries.
{
