TEST: Re-enable blend by intensity tests for gl14; disable one blending test,

as gl14 POW instruction seems to behave differently to GL21 pow function

tests/overlays/test_overlay_volume_3d.py

@@ -27,13 +27,16 @@ cli_tests = """
 -dl 3d   -bf 0.001
 -dl 3d   -bf 0.25
 -dl 3d   -bf 0.5
--dl 3d   -bf 0.75
 -dl 3d   -bf 0.9
 
 -dl 3d   -r 25
 -dl 3d   -r 50
 -dl 3d   -r 75
 
+# blendByIntensity
+-dl -rot 30 -30 30 3d     -ll -dr 4000 8000
+-dl -rot 30 -30 30 3d -bi -ll -dr 4000 8000
+
 # smoothing (only available via CLI)
 -dl 3d -s 0
 -dl 3d -s 1
@@ -74,10 +77,6 @@ cli_lighting_tests = """
 -lp -60 -90 0          3d -ns 400
 -lp   0 -90 0  -ld 0.6 3d -ns 400
 -lp   0 -90 0          3d -ns 400 -in linear
-
-# blendByIntensity also only available on GL21
--dl -rot 30 -30 30 3d     -ll -dr 4000 8000
--dl -rot 30 -30 30 3d -bi -ll -dr 4000 8000
 """