postgresql91 build with libxml

[Phillip Rulon <prulon%gmail.com@localhost>]

Greetings All,
  I'm trying to get postgresql to support xml data.  The psql client
complains that I haven't given --with-libxml during the build.  The
simple minded fix I tried was to edit
databases/postgresql91/Makefile.common and add a line:

CONFIGURE_ARGS+=        --with-libxml

in the section containing all the other CONFIGURE_ARGS stuff. Then
$ make
  ...lots of other configure stuff...
checking for xmlSaveToBuffer in -lxml2... no
configure: error: library 'xml2' (version >= 2.6.23) is required for XML support
...
$ pkg_info libxml2
Information for libxml2-2.7.8nb3:

Comment:
XML parser library from the GNOME project
...etc, etc.

So the library is installed and version is OK, but I'm baffled as to
how to integrate it to the postgresql build setup.  Do I need to alter
the .buildlink hierarchy?  or is there another hack that I've missed.

Any comment greatly appreciated.

thanks,
Phil Rulon