Let CPAN::Uploader load the config

This lets it handle the newly-supported situation where the .pause
file is GPG-encrypted.
cpan uploader trial?
assert that there are no errors while testing the tester

[rt.cpan.org #56831]
use Class::Load, not Class::MOP, for load_class
provide a better error when @Filter fails to load a bundle

[rt.cpan.org #56831]
if a plugin sets dynamic_config to 1, it stays on

Any kind of dynamic configuration should make the whole dist
dynamically configured.  We don't want it turned off because some
other plugin claims not to be.  Maybe this is a mistake, and we
will later revert this so that a plugin can return 0 to override
a previous decision, but it seems highly unlikely.
require bugfixed Archive::Tar::Wrapper
allow "already assign to VERSION" to be fatal
install with cpanm by default (for now)
PkgVersion: Don't attempt to save if file unchanged

PkgVersion always attempted to save the file, regardless whether
it had changed. Now, we track whether the file was successfully
munged, and only save if so. This is an optimization for the
case where no changes are made.