x11-toolkits/gtksourceview2 is broken

[Walter Hurry]

FreeBSD 9.1-RELEASE on amd64

This afternoon I upgraded textproc/libxml2 from version 2.7.8_5 to 
version 2.7.8_0 (at least I think it's libxml2 that's the problem - I 
upgraded py27-libxml2 and gdk-pixbuf2 at the same time).

Then x11-toolkits/gtksourceview2 would not compile. I got the following 
error:

  CCLD   test-widget
../gtksourceview/.libs/libgtksourceview-2.0.so: undefined reference to 
`xmlTextReaderRelaxNGValidate'
gmake[2]: *** [test-widget] Error 1

Sure enough, I see a similar error when I try to open a shell script with 
gedit:

/usr/local/lib/libgtksourceview-2.0.so.0: Undefined symbol 
"xmlTextReaderRelaxNGValidate"

Where do I go from here?