Add pw_justlaunched to tell modders when a player launches from a slope

Merged colette requested to merge fickleheart/SRB2:pw-justlaunched into next

What it says on the tin. 0 == not launched this tic, 1 == launched off a standard slope this tic, 2 == launched off a half-pipe this tic. Doesn't really need the full integer range of a powers fields, but neither does a lot of stuff in there and this was easier than adding a unique field.

Edited by colette

Merge request reports