how to correct corrupted ports tree?

[Gary Aitken]

so, after updating bios, repartitioning, etc,
things seem to be stable, modulo the following:

decided to rebuild ports for peace of mind,
but my basic ports tree is hosed:

    # portmaster -t --clean-distfiles
    ...
    "/usr/ports/Mk/bsd.php.mk", line 335: Malformed conditional (${_USE_PHP_VER${PHP_VER}:Myes} != "")
    ...
    make: fatal errors encountered -- cannot continue

    ===>>> No DISTINFO_FILE in /usr/ports/lang/php4-extensions

    "Makefile", line 20: Could not find /usr/ports/mail/enigmail-thunderbird3/../enigmail/Makefile
    make: fatal errors encountered -- cannot continue

Sure enough:

# ls /usr/ports/lang/php4-extensions
CVS             Makefile        pkg-descr

I didn't see anything in the handbook about how to get the ports tree itself
back to a sane condition.  Do I have to blow the whole thing away and do a
fresh extract?  I don't see a way to force refetch of the actual ports files
like "distinfo" when portsnap thinks the port is up to date.

Gary