EIP 2604: Conditional EXTBALANCE Repricing

Renaming opcodes, includes this one, is also proposed by EIP-1803: Rename opcodes for clarity (Correction: it seems this particular renaming didn’t made it into the forum/EIP, but was discussed on Gitter post-Istanbul)

However as discussed during past ACD calls, this is not part of hard forks, just adopted by tooling.