Add warnings for autogen.sh. Fix AC_CONFIG_SRCDIR.
Update obsolete AC macros.
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)
[Qt] add more NULL pointer checks in bitcoingui

- add missing checks for clientModel and optionsModel
- small cleanups for an #ifdef on Mac
- remove an unneeded else
- small layout changes for if clauses