error out if PORTSDIR is not set to the real directory.

[RD Thrush]

My PORTSDIR is on an nfs server.  Mounting the particular nfs directory on 
/usr/ports (and setting PORTSDIR accordingly) fails the new test in bsd.port.mk.

Apparently test -h considers an nfs mount the same as a symlink...
The attached diff fixes the problem for me.
Index: bsd.port.mk
===================================================================
RCS file: /a8v/pub2/cvsroot/OpenBSD/ports/infrastructure/mk/bsd.port.mk,v
retrieving revision 1.1161
diff -u -p -u -p -r1.1161 bsd.port.mk
--- bsd.port.mk 22 Mar 2012 14:08:50 -0000      1.1161
+++ bsd.port.mk 23 Mar 2012 10:52:43 -0000
@@ -2245,8 +2245,8 @@ ${_BULK_COOKIE}:
 
 ${_WRKDIR_COOKIE}:
        @rm -rf ${WRKDIR}
-       @if test -h ${PORTSDIR}; then \
-               echo 1>&2 "Fatal: ${PORTSDIR} is a symlink. Please set to the 
real directory"; \
+       @if ! test -d ${PORTSDIR}; then \
+               echo 1>&2 "Fatal: ${PORTSDIR} is a not a directory."; \
                exit 1; \
        fi
        @mkdir -p ${WRKDIR} ${WRKDIR}/bin ${DEPDIR}