Giant mushroom dig type

[BrianGaucher]

Digging out giant mushrroms is painfully long. Here is my suggestion
on line 498, 506, and 514
change
groups = {oddly_breakable_by_hand=1},
to
groups = {oddly_breakable_by_hand=1, choppy=1},
Axes make sense for mushrooms, unless you want
groups = {oddly_breakable_by_hand=1, snappy=1},