busctl: add options to control message header flags when invoking methods
busctl: add --timeout= option to specify method call timeout
man: add emacs header to get correct indention in nxml-mode for the manpage XML files that use 2ch indenting

In the long run we really should figure out if we want to stick with 8ch
or 2ch indenting, and not continue with half-and-half. For now, just
make emacs aware of the files that use 2ch indenting.
man: don't mix 2ch and 8ch indentation in busctl.xml