Dump evicted keys when using find_or_insert(pointer).

[jiashuy]

As users want to dump evicted keys when using API find_or_insert(pointer), changes to internal kernels is necessary, and we need to decide the form of interface:

1. Templated member function Templated member function will avoid frequency changes, and we already benefits from the templated member function for_each
2. New optional parameter for current member function find_or_insert(pointer).
3. New overloaded member function find_or_insert(pointer).