In feh_parse_option_array, when a hold-action is set from a theme it would
behave differently than one set from commandline.

Theme: ;;foo would become foo (incorrect)
cmdline: ;;foo would become ;foo (correct)

I doubt anybody would ever have noticed it, since ;foo is a shell syntax error
anyways, but it's definitely better to be on the safe side.

When executing an action starting with a semicolon, feh will
not skip to the next slide. The semicolon is not passed on to
the executing shell, of course. This is kinda ugly, but at least
it makes action handling somewhat more flexible.

Option --action-hold-slide. If specified, when in slideshow mode images will not automatically change after running user action. Otherwise, slideshow images will cycle after action as usual.