rebuilding Gnome without complete erase

[Rod Butcher <rbutcher hyenainternet com>]

I run an unstable Gnome under /usr, which I periodically rebuild from 
cvs head - the idea is that if I use it for regular work I'm more likely 
to detect any bugs. I just update source from cvs and recompile and 
install on top of old versions. Can I assume that old versions of libs 
that stack up will just become unused, and that any new builds will 
automatically link against the latest lib versions ? Or do I really need 
to erase the whole environment before a rebuild to ensure that all 
running Gnome components are indeed the latest ? Or is there a relibale 
uninstall mechanism ?
thanks
Rod
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