test_crypto.c is pretty big; it wouldn't hurt to split it up some
more before I start adding stuff to the PRNG tests.

This is the second part of refactoring the random-int-in-range code.

Some of the code for getting a random value within a range wants to
be shared between crypto_rand() and the new crypto_fast_rng() code.

I don't know how this got here, but this kind of a wrapper only
belongs in a header file.

Using an anonymous mmap() is a good way to get pages that we can set
kernel-level flags on, like minherit() or madvise() or mlock().
We're going to use that so that we can make uninheritable locked
pages to store PRNG data.

Fixes bug 29169.

(It was added in 0.3.5)

"ours" merge to avoid dropping non-broken changes files after
removal of merged 0.2.9 changes files.

Many of these files cause check-changes to fail, which will be a
long-term problem as we continue to support 0.2.9.

George Kadianakis authored 6 years ago and Nick Mathewson committed 6 years ago

We fix it by disabling the scheduling of actual padding.
Fixes #29122.