[Dovecot] convert-tool skip_dotfiles is not the actual option

Looking at the source for convert-tool.c, I see this:

"Usage: <username> <home dir> <source mail env> <dest mail env>\n"
" [skip_broken_mailboxes] [skip_dotfiles] [alt_hierarchy_char=<c>]"

else if (strcmp(argv[i], "skip_dotdirs") != 0) set.skip_dotdirs = TRUE;

Looks like the usage line needs to be fixed (dovecot-1.2-0.rc2).