[PATCH] test: use (format "%S") to print nil in emacs test.

[david@tethera.net]

From: David Bremner <bremner@debian.org>

The behaviour of "emacsclient --eval nil" changed from emacs23 to
emacs24, and in emacs24 it prints 'nil' rather than an empty string.

(format "%S" foo) produces a sexpr form of foo, and is consistent
between the two versions.
---

This fixes another test failure on emacs24. 

I guess maybe all test_emacs output could be canonicalized this way,
but I suspect that would be pretty disruptive.

 test/emacs-subject-to-filename |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/test/emacs-subject-to-filename b/test/emacs-subject-to-filename
index 176e685..a0ffdfe 100755
--- a/test/emacs-subject-to-filename
+++ b/test/emacs-subject-to-filename
@@ -8,10 +8,10 @@ test_emacs '(ignore)'
 
 # test notmuch-wash-subject-to-patch-sequence-number (subject)
 test_begin_subtest "no patch sequence number"
-output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
-      "[PATCH] A normal patch subject without numbers")'
+output=$(test_emacs '(format "%S" (notmuch-wash-subject-to-patch-sequence-number
+      "[PATCH] A normal patch subject without numbers"))'
 )
-test_expect_equal "$output" ""
+test_expect_equal "$output" '"nil"'
 
 test_begin_subtest "patch sequence number #1"
 output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
-- 
1.7.10.4