Small fix for port vtk43
vtk43 just committed requires outdated expat.5. This will
cause the build to fail if expat.6 is installed. I've been
running caret (an application that depends on vtk43) with
expat.6 for several weeks without any apparent problems.
Suggest updating the vtk43 LIB_DEPENDS to allow expat.5 or
Submitted by: Jason Bacon <email@example.com>