Now that we have flat bitmap bit counting functions, we can easily assert that
nfree is always correct. While we're tightening up this code, enforce
consistency on API boundaries as well.
Using an edata_t both for hugepages and the allocations within those hugepages
was convenient at first, but has outlived its usefulness. Representing
hugepages explicitly, with their own data structure, will make future
development easier.
