Patch to add logging of HTTP traffic to soap_server.module

I had a weird problem at work this week, where I couldn't figure out why soap_server was parsing a message in an unexpected way. It turned out that due to the way SoapServer deals with SOAP envelope headers it was attempting to call functions that didn't exist.

I added logging of SOAP HTTP POST body data to the module which helped a lot in tracking that bug down. I've attached it in the patch, hopefully it's of use to someone.