More fixes.
 * Slag now processed in recycling correctly.
 * Slag puddles with no materials in them have the same melting point as plastic.
 * Ore Redeemer skips slag.
Merge branch 'Bleeding-Edge' of github.com:d3athrow/vgstation13 into slag-fixes
Fix slag not cooling via foam
Merge pull request #1854 from N3X15/slag-fixes

More slag fixes.