Problem: The code used safeTransfer when closing an auction, which
may fail due to token restrictions. Failure to close an auction is
a DoS vector.

Solution: If transferring out is not possible, track debt and allow
the auction winner to withdraw funds later.

Problem: There's a potential for cross-function reentrancy in
RiskFund, ProtocolShareReserve, Shortfall contracts arising from
the fact that nonReentrant modifier is not present in all external
functions open to anyone.

Solution: Use nonReentrant where applicable. Follow checks-effects-
-interactions when emitting events.

Problem: We have a view function getPoolAssetReserve that checks
whether the supplied arguments are valid. Compiler-generated
function duplicates the functionality and adds some gas overhead
to function dispatching.

Solution: Make poolsAssetsReserves internal so that we don't have
a compiler-generated version anymore.

Problem: With the evolution of the code, the meaning of the
conversion threshold started to change. As a result, we ended up
comparing the amount out (in tokens), balance of underlying *
oracle price (in dollars), with minAmountToConvert. While in most
cases these values would be close to each other as long as some
stablecoin is used for the threshold, it might be problematic
to set this threshold correctly, considering the potential slippage.

Solution: Expect amountOutMin * base price to be greater than
minAmountToConvert. Adjust the failing test accordingly.

Problem: OpenZeppelin safeApprove implementation is deprecated, so
its usage was removed from the RiskFund contract in favor of plain
approve call. However, this is not the correct way to fix the issue
since the updated version of the code doesn't handle the case when
tokens return false to indicate an error.

Solution: Use a custom library similar to Uniswap's TransferHelpers
to make an approve call supporting:
  * false to indicate failure
  * revert to indicate failure
  * non-compliant tokens that don't return any value