dkms can destroy auto generated headers in some environments

I find that sometimes when I build in a chroot as root on lucid, that dkms has a tendency
to descend into the system's header files and run 'make mrproper'. dkms is assuming that
the sourcecode is there, in an attempt to sanitize the build environment before beginning
the build. This can never complete because on a normal ubuntu system/chroot, the kernel
sources aren't normally present, you only need the headers to compile external modules.

While this step is well intentioned, dkms can never really assume the purpose of
any kernel source tree it's presented. It doesn't know that perhaps there's some active
development going on that tree. It's safer for the system as a whole to not perform this
step at all, or the "clean sources after build" step with the perspective being that should
the dkms build fail for any reason, at least the system is in no worse state than when it
started.

In these interests, I would ask that --no-prepare-kernel --no-clean-kernel be the default
behavior of dkms.