Gas warning for fallback function

[chriseth]

https://www.pivotaltracker.com/story/show/114641125

[axic]

@chriseth The gas estimator output includes an estimate for the fallback. I think this issue is more suitable for the static analyzer, which could issue a warning if the estimate is above 2300.

[axic]

Is this still needed or covered by the remix static analyzer?

[chriseth]

This has been implemented in the remix static analyzer.

[chriseth]

Perhaps to document here: The reason we did not add it to the compiler itself is because gas estimation can only be done after we have the final code and at that point, it is hard to generate an error or warning.

[axic]

I think this can be done in a manner similar to #8008.

[axic]

The reason it may not be a good idea to add:

1. the gas estimator may not be correct at all times
2. if the warning cannot be switched off, users could be annoyed if it is intentionally using more
3. if we are trying to demote the send/transfer process, may be it is not important to highlight this (as we would suggest users to always send appropriate gas)

[chriseth]

I think this is outdated by now.