Make Claws Mail save local/POP emails in its dot-directory.

The default is to save them at ~/Mail, which isn't included in our
current Claws Mail persistence preset.

config/chroot_local-includes/etc/skel/.claws-mail/accountrc.tmpl

@@ -67,7 +67,7 @@ recvtype=3
 #mailbox name if pop3 or local
 #relative path from the user's home
 #default is "Mail"
-#mailbox=
+mailbox=.claws-mail/Mail
 
 #whether to use ssl on STMP connections
 #default is 0, 1 is ssl, 2 is starttls