fix compile issue with missing min() in wallet.cpp
fix compile issue with missing min() in wallet.cpp

BWallet/sx,tuomassiren/libbitcoin-explorer,GroestlCoin/libgroestlcoin-explorer,libmetrocoin/libmetrocoin-explorer,GroestlCoin/libgroestlcoin-explorer,libtetcoin/libtetcoin-explorer,BWallet/sx,libtetcoin/libtetcoin-explorer,tuomassiren/libbitcoin-explorer,libmetrocoin/libmetrocoin-explorer,cancoin/libbitcoin-explorer,cancoin/libbitcoin-explorer,BWallet/sx,GroestlCoin/libgroestlcoin-explorer