hardcoded paths in makefile prevent using checkinstall

[RonnyPfannschmidt]

sudo checkinstall fails after a make due to hardcoded paths
this prevents installing as normal package from the repo

[catamorphism]

Not critical for 0.6, de-milestoning

[bstrie]

@catamorphism, is it safe to presume that rustc itself will start using rustpkg at some point? If so, is it enough to provide an uninstallation facility with rustpkg, or would it still need to be able to work through checkinstall?

[catamorphism]

@bstrie Yes -- #2237 is already open to move rust to being built with rustpkg. That won't be done for a while, but in the meantime, this particular issue doesn't seem super urgent, so it doesn't seem worth it to fix the Makefiles.