xmp: fix compilation on 10.6
libev: remove libevent compatibility header file

This file conflicts with the actual libevent; if someone actually needs
this it can be reinstated as an optional install.

Closes #17921.
dvdauthor: depends_on :libpng

Fixes #18001.
Only fails_with compiler version for developers.

Actually works properly now.

This reverts commit a0e56345ea55f7ee3c41d6bf13f9cfb3af635323.
brew: move to Library/brew.rb

This reverts commit ac156b36d00ead5f225389f0a1d8069d0c1cce4a.
brew: use a shell wrapper script for brew

This reverts commit dfd4dd12a41e1697ee9d5feac12cc1ea7c3a590e.

Fixes the problems from #17683 and #17685.
README: Add Kickstarter link.

Closes #17963
exiftool 9.20
audit: don't complain about versioned automake depending on autoconf