This is primarily a bug fix update.  From the Changes file:

1.7 Tue Jul 18 19:45:00 2006

        - Following some useful e-mail discussions with Mark Linimon
          and Dan Langille, switch to using the MASTER_PORT variable
          to detect master/slave relationships between ports.
          MASTER_PORT will be set in every slave port whereas
          MASTERDIR doesn't have to be.  Here a slave port is one
          defined as using port metadata from some other port, and
          doesn't have to go as far as requiring both master and slave
          to use the same Makefile and other ports infrastructure.

1.7 Sat Jul 22 20:13:00 2006

        - Keep track of the version of the software used to create the
          cache, and prompt for a cache rebuild if the software has
          been upgraded since.  A cache rebuild is definitely required
          for the 1.6 -> 1.7 update.

1.7 Sun Jul 23 10:56:00 2006

        - Don't quit on errors parsing make variables at the cache-init
          or cache-update stage.  Print copious error messages, but carry
          on processing.  Entries for ports that fail at this stage will
          not be created in the cache.

There will be a number of error messages similar to the following when
running cache-init or cache-update:

FreeBSD::Portindex::Port:new_from_make_vars():/usr/ports/emulators/linux_base-gentoo-stage1(linux_base-gentoo-stage1-2006.0_2) -- warning MASTER_PORT=/usr/ports/emulators/linux_dist-gentoo-stage1/ not in expected format

These are warnings only, and no cause for alarm. This release of
FreeBSD::Portindex works around the problem and inserts a corrected
value into the cache.