tests/test-update-reverse

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

hg init
touch a
hg add a
hg commit -m "Added a" -d "1000000 0"

touch main
hg add main
hg commit -m "Added main" -d "1000000 0"
hg checkout 0

echo Main should be gone
ls

touch side1
hg add side1
hg commit -m "Added side1" -d "1000000 0"
touch side2
hg add side2
hg commit -m "Added side2" -d "1000000 0"

hg log

echo Should have two heads, side2 and main
hg heads

echo Should show "a side1 side2"
ls

hg update --debug -C 1
echo Should only show "a main"
ls