[PATCH] test: don't bail out of `run_emacs' too early when missing prereqs

[Pieter Praet]

When running the Emacs tests in verbose mode, only the first missing
prereq is reported because the `run_emacs' function is short-circuited
early:

  #+begin_example
    emacs: Testing emacs interface
     missing prerequisites: [0]  emacs(1)
     skipping test: [0]  Basic notmuch-hello view in emacs
     SKIP   [0]  Basic notmuch-hello view in emacs
  #+end_example

This can lead to situations reminiscent of "dependency hell", so instead
of returning based on each individual `test_require_external_prereq's exit
status, we now do so by checking $test_subtest_missing_external_prereqs_:

  #+begin_example
    emacs: Testing emacs interface
     missing prerequisites: [0]  dtach(1) emacs(1) emacsclient(1)
     skipping test: [0]  Basic notmuch-hello view in emacs
     SKIP   [0]  Basic notmuch-hello view in emacs
  #+end_example

Also add missing prereq for dtach(1).

---
 test/test-lib.sh |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/test/test-lib.sh b/test/test-lib.sh
index 82767c0..6ec3882 100644
--- a/test/test-lib.sh
+++ b/test/test-lib.sh
@@ -907,8 +907,10 @@ EOF
 
 test_emacs () {
 	# test dependencies beforehand to avoid the waiting loop below
-	test_require_external_prereq emacs || return
-	test_require_external_prereq emacsclient || return
+	test_require_external_prereq dtach
+	test_require_external_prereq emacs
+	test_require_external_prereq emacsclient
+	test -z "$test_subtest_missing_external_prereqs_" || return
 
 	if [ -z "$EMACS_SERVER" ]; then
 		server_name="notmuch-test-suite-$$"
-- 
1.7.8.1