When the deprecated option "user-agent" was set to something different
than its default value, said option would always precede and overwrite
the ordinary user_agent option (regardless of whether it was explicitly
set) which leads to a leak of the user_agent option (which has a default
value, so the leak happens always).
Fix this by setting the same destination for both options; the last
option applied wins then.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>