Add require messages to all require statements.

[MicahZoltu]

Trying to integrate with Maker is proving to be quite the chore because many of the require calls contain no message, which means when a transaction fails it is for an opaque reason. If each of the require statements contained a unique message (even if it was just file/line number) then it would be much easier to debug failures.

[gbalabasquer]

Hey, have you checked the latest version? 6fa5581

[MicahZoltu]

Ah, sneaky buggers. I was using the version from yesterday.

[MicahZoltu]

I will re-open if I find any missing after updating to latest.

[gbalabasquer]

There are some missing messages (for internal functions) as that brings issues with the formal verification proofs. Those will remain as they are.