Clean up CMerkleTx::SetMerkleBranch.

The case SetMerkleBranch(NULL) was never actually used, and thus the
involved code (loading the block from disk) can be removed and the
implementation simplified.
Add warnings for autogen.sh. Fix AC_CONFIG_SRCDIR.
Update obsolete AC macros.
qt: Change splash screen to normal window

Makes it possible to move, minimize, unminimize the window while
Bitcoin Core is initializing.
[Qt] include and file header cleanup

- alphabetical ordering
- correct ordering own headers before normal headers etc.
build: fix release name strings for gitian builds

When building from a distdir as gitian does, checking for the .git dir
is not reliable. Instead, ask git if we're in a repo.
Fixing condition 'sabotaging' MSVC build
Also create pid file in non-daemon mode

Always make a pid file, not only when `-daemon` specified.

This is useful for troubleshooting, for attaching debuggers and loggers
and such.

- Write the pid file only after the datadir lock was acquired
- Don't create or remove a pid file on WIN32, and also don't show the option
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.
Fixing improper input syntax and failing bounds check
Merge pull request #4952

01c2807 Add warning about the merkle-tree algorithm duplicate txid flaw (Peter Todd)
Merge pull request #4941

a49f11d qt: Change splash screen to normal window (Wladimir J. van der Laan)
remove code below asserts in limitedmap.h (fixes a ToDo)
qt: Make splash and shutdown window ignore close events

It's strange to be able to close these windows while there is work
in progress.

Also set Qt::WA_DeleteOnClose on both windows to make sure that they
are deleted eventually, no matter what happens.
Merge pull request #4951

d6712db Also create pid file in non-daemon mode (Wladimir J. van der Laan)
Merge pull request #4947

6134b43 Fixing condition 'sabotaging' MSVC build (ENikS)
Merge pull request #4852

5e83bc4 [Qt] include and file header cleanup (Philip Kaufmann)
Merge pull request #4787

4b0deb3 Clean up CMerkleTx::SetMerkleBranch. (Daniel Kraft)
build: change cdrkit location in build-process.md

The cdrkit.org domain expired.
Thanks to gdm85 on IRC for reporting this.
Merge pull request #4765

e2a98d2 Update obsolete AC macros. (randy-waterhouse)
e543811 Add warnings for autogen.sh. Fix AC_CONFIG_SRCDIR. (randy-waterhouse)