Make -reindex cope with out-of-order blocks
Make -reindex cope with out-of-order blocks

Remember out-of-order block headers along with disk positions. This is
likely the simplest and least-impact way to make -reindex work with
headers first.

Based on top of #4468.

(cherry picked from commit ad96e7ccd94679d9125a436ceb5b476aacdfca82)

# Conflicts:
#	src/main.cpp

reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin