Potential overflow in day limit tracking

[joshuahannan]

When a transaction is executed, the amount of tokens in question are accounted for in the currentSpend mapping. Such increment is done with a simple + operator and is hence susceptible to an overflow, especially for non ether transactions. As a result of an overflow, token transfers above majorThreshold could be considered minor transactions and require an incorrect number of confirmations.
Consider using BasicMathLib’s plus function when incrementing such values.

[joshuahannan]

we get stack limit if we do this so we'd either need to not care about it or change to using SafeMath.