I'm crazy so I will add this... pthread rwlock wrappers, along with autoconf stuff...

I'm crazy so I will add this... pthread rwlock wrappers, along with autoconf stuff that detects the presence of the initializer and the ability to set the kind of lock (in our case we rather like writer preferred locks so writer starvation doesn't occur... but on something like Darwin we don't get that)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@46935 65c4cc65-6c06-0410-ace0-fbb531ad65f3