message: reactor.tests.filesystem: Fix compile.
diff: @@ -240,7 +240,7 @@ namespace xorfs
  write(elle::ConstWeakBuffer buffer, size_t size, off_t offset) override
  {
  lseek(_fd, offset, SEEK_SET);
  - for (int i = 0; i < buffer.size(); ++i)
  + for (uint64_t i = 0; i < buffer.size(); ++i)
  const_cast<elle::Byte&>(buffer.contents()[i]) ^= 0xFF;
  return ::write(_fd, buffer.contents(), size);
  }
  