sprites: fix up barrel and octo deaths.

The base of the barrel remained consistent in its last two frames, causing it to seem very static and unaffected before suddenly disappearing. This adds a bit more of a gradual disintegration.

The octaminator has a few fixes:
- the tentacle suddenly appearing behind it in the final frame didn't look right. It's been reduced and a hint of it is given in the preceding frame.
- the antepenultimate frame show the right shoulder falling much further to the side than the frame after it shows. That arm is moved closer to the centre.
- got rid of some of the pillow shading on the right front tentacle-leg in the last two frames.

buildcfg.txt

@@ -1463,9 +1463,9 @@ SKELL7L3	15	61
 SKELL8L2	22	62
 SKELM0	32	54
 SKELN0	30	50
-SKELO0	27	34
+SKELO0	25	34
 SKELP0	30	24
-SKELQ0	32	21
+SKELQ0	32	19
 FATBA1	11	16			; revenant rocket
 FATBA2A8	15	15
 FATBA3A7	17	15