Merge pull request #77 from domob1812/prune-namelist

Implement pruning of nameindex.
Optimise name_list to not require the spent type.

Rewrite name_list's detection of dead players to not depend on the
spent-type array in the CTxIndex.  This makes it work without any disk
accesses at all (not even the tx index).
Ignore some annoying warnings.
Use the optimised name_list also for the Qt UI.

Use the same optimised algorithm of name_list also in the Qt UI.