Disco Dingo is now open for development

[Matthias Klose]

Disco Dingo is now open for development, with the syncs from unstable
done and built.  The development version starts with only a few changes:

 - Python 3.7 is now the default Python3 version, and the only supported
   Python3 version.

 - Perl was updated to version 5.28

 - Merged-usr is now the default in Disco for new installations only.
   It means that /bin is a symlink to usr/bin, similarly /lib and /sbin.
   Existing systems, upon upgrade, will not be reconfigured for
   merged-usr. Care needs to be taken to ensure that both merged-usr and
   split-usr systems are continued to be supported. For example apparmor
   rules may need to be adjusted to use {,/usr}/bin/touch and similar.
   Please use debootstrap from cosmic or later, until the pending SRUs
   are approved.

 - OpenSSL 1.0 removal. It is expected that OpenSSL 1.0 will be removed
   from Disco release, with OpenSSL 1.1.1 LTS as the only provided
   OpenSSL ABI.

Please check your uploads in a disco chroot, don't just test in a cosmic or
bionic environment.  See [1 or [2] how to setup such a development chroot.

-- 
[2] https://wiki.ubuntu.com/SimpleSbuild
[3] https://wiki.ubuntu.com/DebootstrapChroot