Function state mutability can be restricted to pure

[e11io]

Addresses the issue on truffle compile:

zeppelin-solidity/contracts/ownership/HasNoTokens.sol:20:3: Warning: Function state mutability can be restricted to pure
  function tokenFallback(address from_, uint256 value_, bytes data_) external {

[frangio]

Thanks for the suggestion @e11io. 😄

The warning is annoying, but the function is left non-pure because it's meant to define a default behavior that can be overriden in a possibly non-constant way. Constant functions cannot be overriden by non-constant ones.

This is not ideal, but it means we cannot make the function pure.

[BlinkyStitt]

That's good to know, @frangio. Is there some way to silence these warnings? I know you can silence things with solhint, but I'm not sure about solc.

We should be careful not to fix them with #1346

[frangio]

I don't think there is a way to silence these warnings. 😞