message: add BITCOIN_CASH #define
diff: #ifndef BITCOIN_CLIENTVERSION_H
  #define BITCOIN_CLIENTVERSION_H
  +#define BITCOIN_CASH
  +
  #if defined(HAVE_CONFIG_H)
  #include "config/bitcoin-config.h"
  #else
  #endif //HAVE_CONFIG_H
  +/** Client flavor */
  +
  /**
  * Converts the parameter X to a string after macro replacement on X has been performed.
  * Don't merge these into one macro!
  