setup 2.894 release candidate - please test

[Jon Turney <jon.turney@dronecode.org.uk>]

A new setup release candidate is available at:

   https://cygwin.com/setup/setup-2.894.x86_64.exe (64 bit version)
   https://cygwin.com/setup/setup-2.894.x86.exe    (32 bit version)

Please test and report any problems here.

Changes compared to 2.893:

- Drag setup into the 1990s, by replacing the custom-drawn package 
chooser with a ListView common control.

-- Use standard UI elements to choose an action to take on a package or
category, rather than the weird UX of clicking to cycle around a list of
options of undisclosed length.

-- Behaviour change: previously, a category action only affected 
packages which matched any name search filter applied.  Now all packages 
contained by the category are affected.

-- Category view now shows a count of packages in a category

-- Add long description as a tooltip for description

- Add support for ZStandard compression for packages and .ini files

- Fix a new warning reported by gcc 8

- Avoid a potential crash when checking for cached packages
   Addresses: https://cygwin.com/ml/cygwin/2018-10/msg00033.html

- Use pkgconfig for build prerequisite checking

- Fix log spam when package vendor is something other than "cygwin"

- Various cleanups

Thanks to Ken Brown and Achim Gratz.