tests/test-gendoc-sv.t

chgserver: make it a core module and drop extension flags

It was an extension just because there were several dependency cycles I
needed to address.

I don't add 'chgserver' to extensions._builtin since chgserver is considered
an internal extension so nobody should enable it by their config.

#require docutils gettext

  $ $TESTDIR/check-gendoc sv
  checking for parse errors