For every nant .build file generated, Prebuild was adding a <copy> task to copy files from the base directory to the bin/Debug or bin/Release and then another copy task which ended up copying everything again into an embedded bin/Debug/bin/Debug or bin/Release/bin/Release directory.
It just so happened that nant 0.91 and probably earlier appeared to contain a bug which stopped those <copy> directives actually doing any copying. However, 0.92 seems to fix this (perhaps [1]) and so nant starts copying a bunch of files on every build that don't actually appear to be needed to perform the compile, at least in the OpenSimulator project.
This patch removes those copy statements and is really for possible comment since I don't know if it breaks other builds (though that seems unlikely with the previous nant bug).
[1] https://github.com/nant/nant/pull/39
[2] http://opensimulator.org
remove <copy> from NAntTarget patch</copy>