Apply clang-format on some infrequently-updated files
test: Fix DoS tests after c74332c

Fix data structure mismatch ... The mind boggles that they were still passing at all.
Add warning about the merkle-tree algorithm duplicate txid flaw

Lots of people read the Bitcoin Core codebase to learn more about
crypto; better to warn about flaws explicitly so they don't blindly copy
the code for other uses and create broken systems.
Merge pull request #4933

20e01b1 Apply clang-format on some infrequently-updated files (Pieter Wuille)
Merge pull request #4950

33a2771 test: Fix DoS tests after c74332c (Wladimir J. van der Laan)
Merge pull request #4952

01c2807 Add warning about the merkle-tree algorithm duplicate txid flaw (Peter Todd)