Start 6.1 release process

[Rik]

Could someone merge the default branch on to the stable branch so that the
6.1 release can start?  While working on bug #57799 (mkdir and rmdir always
return status output), I realized that there is a common code pattern which
is not Matlab compatible.  Fixing it will hit more than 6 functions and
that in turn will require changes to many other files which use these
functions; fixing rmdir alone required changes to 15 other files.  This
feels like too much change immediately before a release so I want to
continue this work, but on the development branch that will become 7.1.

Thanks,
Rik