tests/test-manifest

use 'x is None' instead of 'x == None'

The built-in None object is a singleton and it is therefore safe to
compare memory addresses with is. It is also faster, how much depends
on the object being compared. For a simple type like str I get:

            | s = "foo" | s = None
  ----------+-----------+----------
  s == None | 0.25 usec | 0.21 usec
  s is None | 0.17 usec | 0.17 usec

#!/bin/sh

# Source bundle was generated with the following script.
#
# hg init
# echo a > a
# ln -s a l
# hg ci -Ama -d'0 0'
# mkdir b
# echo a > b/a
# chmod +x b/a
# hg ci -Amb -d'1 0'

hg init
hg -q pull "$TESTDIR/test-manifest.hg"

echo % should be empty
hg manifest

hg co
hg manifest
hg manifest -v
hg manifest --debug
hg manifest -r 0
hg manifest -r 1
hg manifest -r tip

echo % should fail
hg manifest -r 2
hg manifest -r tip tip

hg manifest tip