Merge branch 'ad/sha1-update-chunked' into maint

Apple's common crypto implementation of SHA1_Update() does not take
more than 4GB at a time, and we now have a compile-time workaround
for it.

* ad/sha1-update-chunked:
  sha1: allow limiting the size of the data passed to SHA1_Update()
  sha1: provide another level of indirection for the SHA-1 functions