Set spot to 0 for when osm is voided, then make urns can not be liqui…

…dated in this state

ISSUE-335-02: remove = operator as it's the default (sky-ecosystem#72)

* ISSUE-335-02: remove = operator as it's the default

* change .travis.yml to get better runtimes

Merge pull request sky-ecosystem#61 from makerdao/fix-deal

Fix flop and flap deal conditions to match with flip one

add end to the pot to prevent drips after global settlement starts (s…

…ky-ecosystem#53)

* add end to the pot to prevent drips after global settlement starts

* changing pot cage to set DSR to ONE and to block filing a new one

* remove unnecessary self declaration

Add tick to flop (sky-ecosystem#50)

* add tend to flop to allow restarting auctions without bids

* rename fuss to flop for better clarity

dai.t.sol: update with new hevm address

dai: consistent revert messages

clearer int range condition for slip

cage: bugfixes, type documentation, safe math.

remove unused math