Log Message:
gtk-doc: Depend on source-highlight for highlighting.

The current default of vim (if found) is broken, but the upstream patch to
fix it doesn't work in isolation, and updating to the latest release breaks
other things, so this is currently the least-worst option to unbreak other
packages like poppler-glib unfortunately.

Really this should be a package option and set explicitly rather than
relying on finding random binaries on the system.  Bump PKGREVISION.