kohabug 2105: prevent crash on IE7

kohabug 2105: prevent crash on IE7

Three scripts were incorrect setting the HTTP type
header to 'utf-8' instead of something appropriate
like 'text/html' - Firefox evidentally can ignore that
mistake, but IE7 does not.

Fixed by replacing an invalid print of the HTTP header
and template output with a call to
C4::Output::output_html_with_http_headers.

Also corrected POD in C4::Auth and InstallAuth to
reflect correct use of output_html_with_http_headers.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>