chmod +x for scripts and make the shebang/preamble consistent.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

orchard_empty_roots.py

@@ -1,3 +1,6 @@
+#!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 from orchard_merkle_tree import empty_roots
 from orchard_pallas import Fp
 from tv_output import render_args, render_tv

orchard_map_to_curve.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
 
 from orchard_group_hash import map_to_curve_simple_swu
 from orchard_iso_pallas import Point as IsoPoint

orchard_note_encryption.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 import struct
 
 from chacha20poly1305 import ChaCha20Poly1305

orchard_poseidon.py

@@ -1,3 +1,6 @@
+#!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 from orchard_pallas import Fp
 import numpy as np
 from itertools import chain

orchard_poseidon_hash.py

@@ -1,3 +1,6 @@
+#!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 from orchard_pallas import Fp
 from orchard_poseidon import perm
 from utils import leos2ip

transaction.py

@@ -1,4 +1,3 @@
-#!/usr/bin/env python3
 import struct
 
 from orchard_pallas import (

zc_utils.py

@@ -1,4 +1,6 @@
 #!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 import struct
 
 def write_compact_size(n):

zip_0143.py

@@ -1,4 +1,6 @@
 #!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 from pyblake2 import blake2b
 import struct
 

zip_0243.py

@@ -1,4 +1,6 @@
 #!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 from pyblake2 import blake2b
 import struct
 

zip_0244.py

@@ -1,4 +1,6 @@
 #!/usr/bin/env python3
+import sys; assert sys.version_info[0] >= 3, "Python 3 required."
+
 from pyblake2 import blake2b
 import struct