Better provisions for binary package updates

[Marc Balmer <marc%msys.ch@localhost>]

I need better provisions for binary package updates (pkg_add -u).  Currently, 
all we have is an install script that is called during the installation process 
before and after the package files are installed, with the argument PRE-INSTALL 
and POST-INSTALL.

This does not allow the script to detect an update situation easily, but I need 
that for application that e.g. need to update a database scheme.

The debian apt system knows the maintainerscripts for this purpose, and they 
work nicely.  While the apt mechanism is quite elaborate, I suggest a much 
simpler addition to pkg_add:

If pkg_add is called with the -u option, the install script will be called with 
the additional argument REPLACE.  This allows the script to perform whatever is 
needed for an update while retaining backwards compatability (install scripts 
that are not update aware will behave like before).

Comments, more ideas or suggestions on this?