Can no longer slip if lying or in a vehicle, visible_message slipping
Created by: dylanstrategie
- Slipping on water, lube and ice now check for walking(), which means that you can't slip anymore if you are flying, lying on the ground (useful to avoid sliplocking) and locked to an atom (aka vehicles)
- Added visible_message to all slipping messages
- Trimmed down the slipping procedure itself massively. Human check was completely useless (it wasn't even typecasted) and was removed. Slimes still don't slip. No functional changes and a bunch of copypaste removed
No gameplay changes, just pure issue fixing
Fixes #6276 (closed)