setup 2.910 release candidate - please test

[Jon Turney]

A new setup release candidate is available at:

   https://cygwin.com/setup/setup-2.910.x86_64.exe (64 bit version)
   https://cygwin.com/setup/setup-2.910.x86.exe    (32 bit version)

Please test, and report any problems here.

This is not the place for setup feature requests.

Changes compared to 2.909:

- Add new option '--compact-os [ALGORITHM]' (Thanks to Christian Franke)

Possible ALGORITHM values are 'xpress4k', 'xpress8k', 'xpress16k' and 
'lzx'. If ALGORITHM is omitted, 'lzx' is used.

This enables use of the Windows CompactOs API for filesystem compression 
of installed files which can benefit from it.

- Add new option '--symlink-type TYPE'

Possible TYPE values are 'sys', 'wsl', 'lnk', and 'native'.

This controls the type of Cygwin symlink (see [1]) created by setup and 
post-install scripts.

If this option is absent, the default is determined by any winsymlinks 
setting in the CYGWIN environment variable, or 'sys' if none.

This changes the default behaviour slightly, in that now symlinks 
created by post-install scripts are also of 'sys' type, rather than the 
default type used by Cygwin.

(This addresses certain exotic scenarios such as 
https://cygwin.com/pipermail/cygwin/2020-August/246008.html, where 
Cygwin is being installed into a Docker for Windows container which 
doesn't support WSL symlinks)

- '--quiet' implies 'download and install packages'

'--quiet' now implies 'download and install packages', rather than 
'whatever source mode was chosen in the last run'.

This can be overridden with '--download' or '--local-install'. 
Specifying both already had the meaning 'download and install packages', 
but is now not required in combination with '--quiet' to get definite 
behaviour.

Addresses: https://cygwin.com/pipermail/cygwin/2021-September/249456.html

- Add new option '--lang LANGID'

Changes the GUI language ID from the Windows default.

- Various internal changes to facilitate GUI localization

- An experimental French localization of most GUI text (based on 
translations provided by Eric Laussage)

For instructions on obtaining and building the source code for setup, 
see https://sourceware.org/cygwin-apps/setup.html

[1] https://cygwin.com/cygwin-ug-net/using.html#pathnames-symlinks