[plt-dev] What happened to configure --prefix on MacOS?

Forgive me if this has been discussed elsewhere, but I've been extremely
busy of late and haven't really been reading the PLT lists.

I just did an "svn up" followed by "mkdir build; cd build; ../src/configure
--prefix=$HOME/Applications/plt", only to learn that configure no longer
supports --prefix on OS X.

What's going on here?  How do I do a non-in-place build?  (I see no reason
to keep the .o files and other artifacts of compilation around between
builds, especially since I 'svn up' so infrequently that I always get
changes to the .c files, which according to Matthew requires creating a new
build directory.)

Richard