Fixed a flaw with the toxin filter.

Increased the amount of damage the toxin filter heals to be able to keep up with the damage converter symptom.
Correctly set the values so there's no chance for underhealing

Apparently damage_converter converts 6 or 12 damage, plus the randomness of the symptoms makes it hard to predict.
Made self-respiration use dexalin instead.
Typo fix.
Merge pull request #2278 from Giacom/toxin_filter

Fixed a bug with the toxin filter.