Remove DEFTESTCASE and DEFTESTCASE_SLOW redefinitions
Added tests for addto_lists function
Refactoring of node replacements in addto_lists function

An index for replacement candidate is searched
in one lookup cycle for all types (bad, possibly bad, good).
Sorting of items has been removed (sorting logic can be substituted
by a maximum search).
Tests fix for an original behavior for duplicates
Merge branch 'remove-sort_list' of https://github.com/pyruvate/toxcore
Fixed bug.