Add 'numbering identification' to the dedup pool.

The dedup pool can now be used to allocate elements and identify
them with a number rather than an address.

This new feature is not used (yet) but is intended to be used to
decrease the memory needed to store the CFSI information.




git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14123 a5019735-40e9-0310-863c-91ae7b9d1cf9