Water cools hot turfs even if they do not have a hotspot.

Or rather, it cools the turf's air, which is as close as it gets for SS13.

Also:
* Adjusted fire extinguisher volumes to correspond to the new beaker volumes, and scaled things accordingly. Fire extinguishers carry 120u of water, while the mini extinguishers carry 60. The exosuit mounted extinguisher carries a 500u, or half a water tank. I might increase it to 1000u, to try and make it worth having since since firefighter exosuits aren't needed that often.
* Moved water poisoning slimes from reaction_turf() into reaction_mob()
* Adds a check for reagents to prevent the runtime in #6821. I guess you could say it fixes #6821, although it doesn't address the underlying cause of the reagents holder being null.

Using up an entire extinguisher can cool a medium sized room (such as the one shown below) by 82 C. I'm hoping to strike a balance where the extinguishers are not too good but have enough of an effect to justify using them or to make them useful for small fires.


![screenshot 2014-10-24 19 39 35](https://cloud.githubusercontent.com/assets/242428/4778242/89916e98-5be2-11e4-98e0-89c23fc7cc17.png)

Ditto