build: Use $(PYTHON) instead of python for the keycode map generator

Also prepend $(AM_V_GEN) to the command line, mark virkeycode-mapgen.py
as executable and switch the shebang line from /bin/python to the
commonly use /usr/bin/python.

src/Makefile.am

@@ -90,7 +90,7 @@ EXTRA_DIST += $(srcdir)/util/virkeymaps.h $(srcdir)/util/keymaps.csv \
 
 $(srcdir)/util/virkeymaps.h: $(srcdir)/util/keymaps.csv	\
 		$(srcdir)/util/virkeycode-mapgen.py
-	python $(srcdir)/util/virkeycode-mapgen.py <$(srcdir)/util/keymaps.csv >$@
+	$(AM_V_GEN)$(PYTHON) $(srcdir)/util/virkeycode-mapgen.py <$(srcdir)/util/keymaps.csv >$@
 
 $(srcdir)/util/virkeycode.c: $(srcdir)/util/virkeycode.h $(srcdir)/util/virkeymaps.h
 

src/util/virkeycode-mapgen.py

-#!/bin/python
+#!/usr/bin/python
 
 """
 Generate the big keycodes table for virkeys.