Fix some breakage from the conversion to the FCGX_ API

Commit 6dc0768 ("app: Switch to the FastCGI FCGX_ API") was incomplete.

The Makefile needs to define _HAVE_FCGX so the right bits in
libctemplate get used and we need to use fcgx_out in the TMPL_write()
call in utils.c::send_template()

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>