In recent versions of highlight there can be more than one langdefdir.
This patch fixes the ensuing hilarity when the user adds a single
highlight lang definition and highlight.pm expects all definitions to
be in the same place.
There's a nice message if the plugin is loaded and used and highlight is
not available, and a nice fallback. So no need for this other warning,
which can happen any time all plugins are loaded to generate a setup file.
Note that in particular calling initTheme with and empty file does not
work anymore.
use of initLanguage was replaced by loadLanguage, which seems to work
in both places.
I tried to make it a bit more robust against missing a highlight package.
There are lots of warnings, but it no longer crashes.
Setting up a new highlighter object is slightly expensive since it
reads and parses the langfile each time. So cache them.
This also speeds up ext2langfile by avoiding it needing to check for the
existence of a language file in some cases.
format: Provide a htmlizefallback hook that other plugins can use to
handle formats that are not suitable for general-purpose htmlize hooks.
highlight: Use the hook to allow formatting of any language/extension,
without it needing to be enabled for standalone source files.
highlight: If the highlight perl binding is not available, fallback
safely to a passthrough mode.