tests/test-gendoc-el.t

hgweb: ensure Content-Length and Content-Type are not promoted to HTTP_ on py3

In stabilizing test-lfs-serve-access.t for py3, the server started asserting on
blob upload:

    Environment should not have the key: HTTP_CONTENT_LENGTH (use CONTENT_LENGTH instead)

It could be avoided by explicitly setting the Content-Length header on the
client side.  I didn't go back to py2, but printing the original header here in
py37 revealed 'Content-length' when sent to the error log.

#require docutils gettext

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