tests/test-add.out

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

adding a
? a
adding a
A a
A a
? b
A a
A b
% should fail
b already tracked!
A a
A b
% should fail
a already tracked!
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
created new head
merging a
warning: conflicts during merge.
merging a failed!
0 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg up --clean' to abandon
M a
? a.orig
% should fail
a already tracked!
M a
? a.orig
% issue683
R a
? a.orig
M a
? a.orig
c does not exist!
d does not exist!
M a
A c
? a.orig