Fix "expectedtime" estimate returned by RPC call "getstakinginfo".
Fix "expectedtime" estimate returned by RPC call "getstakinginfo".

It was wrong before, using nTargetSpacing rather than nTargetStakeSpacing, and ignoring current difficulty.

nochowderforyou/clams,Kefkius/clams,dooglus/clams,thunderrabbit/clams,thunderrabbit/clams,thunderrabbit/clams,dooglus/clams,nochowderforyou/clams,Kefkius/clams,robvanmieghem/clams,dooglus/clams,thunderrabbit/clams,robvanmieghem/clams,Jheguy2/Mercury,nochowderforyou/clams,Jheguy2/Mercury,robvanmieghem/clams,dooglus/clams,Jheguy2/Mercury,dooglus/clams,robvanmieghem/clams,nochowderforyou/clams,Kefkius/clams,Kefkius/clams,Kefkius/clams,Jheguy2/Mercury,thunderrabbit/clams,Jheguy2/Mercury,robvanmieghem/clams,nochowderforyou/clams