MSC: int _heapchk( void )

		MSC: int _bheapchk( _segment seg )
		MSC: int _fheapchk( void )
		MSC: int _nheapchk( void )

	- prototype in malloc.h

	- runs consistency check on different heaps
	- heapchk maps to the other functions depending on memory model

	- returns one of the following:

	  _HEAPOK	heap is ok
	  _HEAPBADBEGIN initials allocation header couldn't be found
	  _HEAPBADNODE	heap/node has been damaged
	  _HEAPEMPTY	heap has not been initialized

	- see	heapset()   heapwalk()