STEPattribute member _derive: public, int -> protected, bool
check for redefine in attr being copied _from_, not to - ?!

I do not understand how this could have been right or how it did not
cause problems if wrong. Perhaps redefined attr's are used so
infrequently that it went unnoticed?
move clstepcore cpp test dir into clstepcore
skeleton for the operators/constructors tests for STEPattribute
improve stepattr copy constructor

uses shallow copy, so access violations are possible
test_inverse_attrs2 works now because of the STEPattr copy ctor fix
make some STEPattribute members protected - access via funcs

affects STEPfile, STEPattributeList

protected members acc funcs
don't use RedefiningAttr() within the class, since _redefAttr is accessible
eliminate duplicate error code in STEPwrite()
don't use int as bool
name parameters in declarations
some return types char * --> std::string, eliminate unnecessary const_casts
update asStr() function - return std::string
tests for copy constructor, ShallowCopy()
sameADesc() behaves like old operator==, rewrite operator==
fix ShallowCopy(), copy constructor, destructor
eliminate error and warning in p21read.cc
oops, some STEPattribute constructors didn't initialize all members
oops, need a way to access attr data now that ptr is protected
update tests to work with STEPattribute class changes