Allow ${PACKAGES} to be a symbolic link to another file system with more space.

*** 8.2-RELEASE/ports/Mk/bsd.port.mk.orig	Thu Dec  8 17:48:00 2011
--- new/ports/Mk/bsd.port.mk	Thu Dec  8 17:49:05 2011
***************
*** 3916,3922 ****
  		fi; \
  	fi
  	@if ${PKG_CMD} -b ${PKGNAME} ${PKGFILE}; then \
! 		if [ -d ${PACKAGES} ]; then \
  			cd ${.CURDIR} && eval ${MAKE} package-links; \
  		fi; \
  	else \
--- 3916,3922 ----
  		fi; \
  	fi
  	@if ${PKG_CMD} -b ${PKGNAME} ${PKGFILE}; then \
! 		if [ -e ${PACKAGES} ]; then \
  			cd ${.CURDIR} && eval ${MAKE} package-links; \
  		fi; \
  	else \
--------------