Staging break user account modification in post-install

[Aryeh Friedman]

post-install is now called *BEFORE* users are created (before staging was
added it was after)... looking at bsd.port.mk there seems no reasonable
target that replaces post-install for this purpose.   Namely I need to lock
the user account that was created and assign a default password to it.
This is what I had that used to work:

post-install:
          echo password|pw usermod user -h 0 2>/dev/null
          pw lock user