removed const_cast from bstree, list, and slist
Merge branch 'master' into no-const_cast
Merge branch 'master' into no-const_cast
Merge branch 'no-const_cast' of https://github.com/mateidavid/intrusive into mateidavid-no-const_cast
Fixed #9948: remove use of const_cast in intrusive containers.
Added tests for [s_]iterator_to.