Write 'Persistent-Auth' header to err_headers_out
Write 'Persistent-Auth' header to err_headers_out

In some cases, like internal redirects, authentication is completed but our
'Persistent-Auth' header is dropped by the server because headers_out is ignored
with errors (4xx, 5xx) and internal redirects.

See: https://ci.apache.org/projects/httpd/trunk/doxygen/structrequest__rec.html#a9f49c2d5680987c0c28466ea37d41a62

This fixes #110

Reviewed-by: Simo Sorce <65f99581a93cf30dafc32b5c178edc6b0294a07f@redhat.com>
Reviewed-by: Isaac Boukris <ab5177b42f32473880183450eb7c0834b1c7bfad@gmail.com>
Closes #111

frenche/mod_auth_gssapi,frenche/mod_auth_gssapi,frenche/mod_auth_gssapi,frenche/mod_auth_gssapi