[BUG] completion.commands does not remove multiple commands

[Todd Zullinger <tmz@pobox.com>]

Hi,

I was playing with the completion.commands config added in
6532f3740b ("completion: allow to customize the completable
command list", 2018-05-20) and noticed an issue removing
multiple commands.

I wanted to remove completion for cherry and mergetool, so I
added them both to the config:

    git config completion.commands "-cherry -mergetool"

But git still completes cherry in this case, only removing
mergetool.  Swapping the items in the config yields the
opposite result (cherry is removed and mergetool is not).

With luck this will be a clear and easily resolved issue in
list_cmds_by_config() (in help.c).

Here's an example in test form:

-- 8< --
diff --git c/t/t9902-completion.sh w/t/t9902-completion.sh
index 3a2c6326d8..06cee36ae5 100755
--- c/t/t9902-completion.sh
+++ w/t/t9902-completion.sh
@@ -1483,6 +1483,14 @@ test_expect_success 'git --help completion' '
 	test_completion "git --help core" "core-tutorial "
 '
 
+test_expect_failure 'completion.commands removes multiple commands' '
+	test_config completion.commands "-cherry -mergetool" &&
+	git --list-cmds=list-mainporcelain,list-complete,config |
+		grep ^cherry >actual &&
+	echo cherry-pick >expected &&
+	test_cmp expected actual
+'
+
 test_expect_success 'setup for integration tests' '
 	echo content >file1 &&
 	echo more >file2 &&
-- 8< --

That's not quite normal form for t9902, but I was undable to
create a working test using the test_completion functions.
The tests set GIT_TESTING_PORCELAIN_COMMAND_LIST and
GIT_TESTING_ALL_COMMAND_LIST which override the settings in
the completion script.  I played a bit with adjusting those
to add cherry{,-pick} to the command lists, unsetting those
vars for the test, and such, to no avail.

In the end, I'm not really sure that calling --list-cmds
directly is such a bad way to go for testing this issue.

-- 
Todd