reliable (if somewhat inefficient): make the current time an
attribute of the derivation. Thus, every call to `nix-build' will
cause the find-includes derivation to be re-done (but not the actual
compilations if that's not necessary!). I added a `curTime' primop
to do this.
`findIncludes' function. The current implementation is impure and
therefore not correct: it gathers header file dependencies only once
for a specific path (due to caching).
explicitly. If you forget a dependency, it's simply not visible to
the compiler, and so the compilation fails. This is a big plus over
conventional Make.
