The port still depends on version 1.0 of libpq:

BUILD_DEPENDS=  ${PREFIX}/lib/perl5/site_perl/DBI.pm:${PORTSDIR}/databases/p5-DBI \
                ${PREFIX}/pgsql/lib/libpq.so.1.0:${PORTSDIR}/databases/postgresql

The version 1.0 for libpq is no longer valid for PostgreSQL 6.3.2 as it
now comes with version 1.1.  Therefore the Makefile fails to detect
libpq even though it is installed on the system.

Fix: 

Raise the version number from 1.0 to 1.1 in the BUILD_DEPENDS line.  I
have done this myself and now the port builds correctly again.

One issue needs to be considered though: This fix will break the port
on systems where 6.3.0 (or 6.3.1, I'm not sure) is still installed,
because that version comes with libpq.so.1.0.  Therefore it should be
considered that the PostgreSQL port creates a symlink from libpq.so.1.?
to libpq.so.1 and p5-DBD-Pg depends on libpq.so.1 instead of
libpq.so.1.?

--
             Sascha Blank            | "I prefer to work behind the scenes. The
   Student and System Administrator  | reward is nearly as great,  and the risk
 at the University of Trier, Germany | is far far less" - Ambassador Mollari in
    mailto:blank@fox.uni-trier.de    | in Babylon 5, "The coming of shadows"
How-To-Repeat: 
Try to build this port yourself and watch what happens.