Move WT_HAZARD_INCR to the WT_SESSION_IMPL structure.
Get rid of ENTRY_SIZE (it's not in the right namespace, and it's only used
in one place as a hard-coded constant).
Rework WT_UNUSED/WT_UNUSED_RET slightly: move GNUC macros out of misc.h
into their own include file "gcc.h", change the test programs to include
and use the definitions from that file.