Merge branch 'ld/p4-editor-multi-words'

Unlike "$EDITOR" and "$GIT_EDITOR" that can hold the path to the
command and initial options (e.g. "/path/to/emacs -nw"), 'git p4'
did not let the shell interpolate the contents of the environment
variable that name the editor "$P4EDITOR" (and "$EDITOR", too).
Make it in line with the rest of Git, as well as with Perforce.

* ld/p4-editor-multi-words:
  git-p4: tests: use test-chmtime in place of touch
  git-p4: fix handling of multi-word P4EDITOR
  git-p4: add failing test for P4EDITOR handling

git-p4.py

@@ -1248,7 +1248,7 @@ 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.