Nan is enforcing wrong ~1GB kMaxLength for Nan::NewBuffer, should be 4GB

[Rush]

This resulted in a real-world application issue:

[1] Assertion failed: (size <= imp::kMaxLength && "too large buffer"), function NewBuffer, file nan.h, line 939.

Buffers of 1GB are definitely realistic when dealing with >4k visual data.

The check is implemented here

nan/nan.h

Line 896 in e14bdcd

assert(length <= imp::kMaxLength && "too large buffer");

The constant is defined here:

nan/nan.h

Line 417 in e14bdcd

static const size_t kMaxLength = 0x3fffffff;

I believe it should be 4GB as reported by buffer.constants.MAX_LENGTH (https://nodejs.org/api/buffer.html#bufferkmaxlength)