Summary: Convert mem_hdr to the use of a splay.

Summary: Convert mem_hdr to the use of a splay.
Keywords:

* Add a dataRange() method to mem_node, to allow direct access to the range
  available.
* Add mem_node::deleteSelf().
* Update copyright on stmem.[cc|h].
* Test new mem_node methods.
* Add Splay::end() method and test.
* Add mem_hdr::unlink().
* Remove mem_hdr::unlinkHead(), mem_hdr::getHighest.., mem_hdr::head and mem_hdr::tail.
* Remove mem_node::next.
* Introduce mem_hdr::dump().
* Introduce mem_hdr::size().
* Introduce mem_hdr::start().
* Make mem_hdr::getBlockContainingLocation() public.