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] include and file header cleanup

- alphabetical ordering
- correct ordering own headers before normal headers etc.
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)
Use actually valid transactions for script tests
Add actual signature tests
Grammar fixes in README

Github-Pull: #4956
Fixing out of bounds error in GetKey()
Merge pull request #4962

6f3ae9b Fixing out of bounds error in GetKey() (ENikS)
Merge pull request #4949

c8589bf Add actual signature tests (Pieter Wuille)
76ec867 Use actually valid transactions for script tests (Pieter Wuille)
Merge remote-tracking branch 'bitcoin/master'