git-p4: fix handling of multi-word P4EDITOR

This teaches git-p4 to pass the P4EDITOR variable to the
shell for expansion, so that any command-line arguments are
correctly handled. Without this, git-p4 can only launch the
editor if P4EDITOR is solely the path to the binary, without
any arguments.

This also adjusts t9805, which relied on the previous behaviour.

Suggested-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -1220,7 +1220,7 @@ class P4Submit(Command, P4UserMap):
             editor = os.environ.get("P4EDITOR")
         else:
             editor = read_pipe("git var GIT_EDITOR").strip()
-        system([editor, template_file])
+        system(["sh", "-c", ('%s "$@"' % editor), editor, template_file])
 
         # If the file was not saved, prompt to see if this patch should
         # be skipped.  But skip this verification step if configured so.

t/t9805-git-p4-skip-submit-edit.sh

@@ -90,7 +90,7 @@ test_expect_success 'no config, edited' '
 		cd "$git" &&
 		echo line >>file1 &&
 		git commit -a -m "change 5" &&
-		P4EDITOR="$TRASH_DIRECTORY/ed.sh" &&
+		P4EDITOR="\"$TRASH_DIRECTORY/ed.sh\"" &&
 		export P4EDITOR &&
 		git p4 submit &&
 		p4 changes //depot/... >wc &&

t/t9820-git-p4-editor-handling.sh

@@ -19,7 +19,7 @@ test_expect_success 'init depot' '
 
 # Check that the P4EDITOR argument can be given command-line
 # options, which git-p4 will then pass through to the shell.
-test_expect_failure 'EDITOR with options' '
+test_expect_success 'EDITOR with options' '
 	git p4 clone --dest="$git" //depot &&
 	test_when_finished cleanup_git &&
 	(