[blocking] some mobs are not effected by levitate even when they're on dry land.

Verification builds: Release 924386 - 1.5.0.4 BETA
Summary: using /effect @e levitation it doesn't work on on the following mobs: cod, pufferfish, salmon, squid, tropical fish, wither

Repro Steps:

1. Download the 'super behavior bug test time' (tm) map from Greg on Slack
2. summon any of the listed mobs
3. press the button to levitate things

Observed Results:

1. the mob just sits there like a dumb dumb

Expected Results: the mob should float to the sky like every other mob

Impact: this impacts the release of my map which has been discussed with Greg

Mobs it's bugged on:
cod, pufferfish, salmon, squid, tropical fish, wither