We don't need to add additional components when generating .orig
tarballs for the 4.0.0-rc series.

At least at the moment, uupdate doesn't do the right thing given the
structure of the upstream tarballs, and our need to keep packaging
based on the upstream svn trunk, so remove the script field
altogether.

Use tmpdirs for everything...

Tests run code that creates stuff relative to the user's
~/.spamassassin directory.  Ensure that this doesn't use the actual
home directory, and that we can still run in environments where HOME
is unset.

The spamassassin test suites create sockets relative to the source
directory. In some environments, including Debian's GitLab CI build
environments, the path of the socket exceeds the 108 character limit on
socket names.  We work around this by not being quite so paranoid about path
names when working relative to the source tree as opposed to a

Tests fail if this is not present during build, and it is used by the
Mail::SpamAssassin::Plugin::ResourceLimits plugin