Eliminate any direct extern references to memLow/memHigh

sasindex_tt/sasstringbtree_tt has hot TOC indirect access to memLow/memHigh.
Should change these to visibility( "hidden") to get TOC relative access. But
before that, need to eliminate any direct extern references from test cases.

	* ./src/sassim.cpp (memLow, memHigh): Visability hidden.
	(setSASmemrange): New function.
	* ./src/sassim.h (setSASmemrange): Extern.
	* src/tests/sphlflogger_t.c (setmemrange): Replace direct
	access to memLow/memHigh with setSASmemrange() call.
	* src/tests/sphlockfreeheap_t.c (setmemrange): Likewise.
	* src/tests/sphlogportal_t.c (setmemrange): Likewise.
	* src/tests/sphsinglepcqueue_t.c  (setmemrange): Likewise.