Issue #1195 - Standing at a corner under steam, but far away enough to not be...

Issue #1195 - Standing at a corner under steam, but far away enough to not be impacted by it, causes the player animation to reset for a tic

Instead of using a janky MF_SOLID method, let's make the steam jet an MF_SPECIAL, and allow pushables to trigger P_TouchSpecialThing. This could potentially be expanded in the future to allow pushables to interact with other non-solid objects.