py3: use print as a function in tests/test-walk.t

Differential Revision: https://phab.mercurial-scm.org/D3070

tests/test-walk.t

@@ -519,7 +519,12 b' Test split patterns on overflow'
 
   $ cd t
   $ echo fennel > overflow.list
-  $ $PYTHON -c "for i in range(20000 / 100): print 'x' * 100" >> overflow.list
+  $ cat >> printnum.py <<EOF
+  > from __future__ import print_function
+  > for i in range(20000 // 100):
+  >   print('x' * 100)
+  > EOF
+  $ $PYTHON printnum.py >> overflow.list
   $ echo fenugreek >> overflow.list
   $ hg debugwalk 'listfile:overflow.list' 2>&1 | egrep -v '(^matcher: |^xxx)'
   f  fennel     fennel     exact