forked from boostorg/unordered
structure for unordered_multimap/unordered_multiset that uses an extra pointer per node but makes most operations more efficient when equivalent nodes are present. Now uses macros instead of template metaprogramming to implement the differences between containers with equivalent and unique keys. Removed the erase_iterator stuff which complicated matters more than it helped. Now just using pointers with some helper functions. [SVN r2950]