tests/test-gendoc-pt_BR.t

extensions: include current version in "invalid version" message

It is "not so rare" for the mercurial version to be badly detected at build
time. In such case, version check for extensions gets confused.

To help pinpoint the error, we now include the Mercurial's version number in
the error message.

#require docutils gettext

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