use RTLD_NOLOAD if it's available to make loading dynamic modules a little...

use RTLD_NOLOAD if it's available to make loading dynamic modules a little faster and less resource-intensive
also, keep trying to dlclose() a module until it actually goes away, since it may have other modules it brought in when it was loaded (thanks PCadach for pointing this problem out to me)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@40949 65c4cc65-6c06-0410-ace0-fbb531ad65f3