Use portable #! in python scripts (/usr/bin/env)

contrib/linearize/linearize-data.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # linearize-data.py: Construct a linear, no-fork version of the chain.
 #

contrib/linearize/linearize-hashes.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # linearize-hashes.py:  List blocks in a linear, no-fork version of the chain.
 #