use lazyInstMgr for inverse_attr3.cc
improve comments, a few other small changes that don't affect behavior
include subsuperiterators header
add lazyRefs.h
trivial changes
use lazyRefs in lazyInstMgr
add STEPinvAttrList for inv attr descs and setter/getter pointers

this will allow access to inverse attr values even with late binding, and is necessary to
set these attr values when the instances are being loaded
use STEPinvAttrList in sdaiApplication_Instance
generated c++: static setter/getter for inverse attrs
in generated c++: in constructors, populate iAttrs

is populated with inverse attrs, setters, getters
in generated c++: ensure that pointers are zeroed (DataMemberInitializers())
in generated c++: ensure pointer is non-null before calling shallowCopy
in generated c++: create data members for null pointers
eliminate unused buffer
use InstMgrBase instead of InstMgr in most stepcore classes

this is so that lazyInstMgr functions will be called when necessary
whoops, don't pretend an instance can't be found if it is already loaded
update inverse attr test 3
forgot to replace InstMgr with InstMgrBase in selects.c
when printing initializers, skip derived attrs
forgot to add 'const' keyword in several places after changing the ..._get_head() fn