emacsclient: adjust to new config file location

* lib-src/emacsclient.c (open_config): New arg XDG, to respect
XDG_CONFIG_HOME, consistently with Emacs proper.  Caller changed.
Use XDG convention if available, falling back on the old names
if not.
1 job for master in 54 minutes and 38 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #3157
test-all

00:54:38