startTick == endTick

[kinrezC]

• Fixes maxDutchAuctionTest -- in this test we are swapping for exactly 1 asset, warping +1 epoch, then swapping that 1 asset back in. This causes the netSold to be <= 0 to trigger the max DA test. In this test we were checking that the lowerSlug was unset, but this will not be the case given that when we warp +1 epoch after the first swap we will be partially dutch auctioning down. Because of the partial dutch auction we will not be taking out all of the numeraire token, and thus the lower slug is NOT unset.
• Fixes assetAvailable being passed to _computePriceDiscoverySlug. Previously, we were computing assetAvailable after clearing the slugs and then passing assetAvailable to computeUpperSlugData. In computeUpperSlugData we subtract the asset tokens allocated to the upper slug from assetAvailable, but this operation is done locally in the computeUpperSlugData scope and was not effectively propagated to the parent function call. Now we return a new value assetRemaining from computeUpperSlugData such that we have a correct accounting of the tokens available for the price discovery slugs. (flagged in Check that assetAvailable is correct #103)
• Tests all pass for isToken0 == true