r5941: Commit this patch much earlier than I would normally prefer, but metze needs...

r5941: Commit this patch much earlier than I would normally prefer, but metze needs a working tree...

The main volume of this patch was what I started working on today:
 - Cleans up memory handling around DCE/RPC pipes, to have a parent talloc context.
 - Uses sepereate inner loops for some of the DCE/RPC tests

The other and more important part of this patch fixes issues
surrounding the new credentials framwork:

This makes the struct cli_credentials always a talloc() structure,
rather than on the stack.  Parts of the cli_credentials code already
assumed this.

There were other issues, particularly in the DCERPC over SMB handling,
as well as little things that had to be tidied up before test_w2k3.sh
would start to pass.

Andrew Bartlett
(This used to be commit 0453f9d05d2e336fba1f85dbf2718d01fa2bf778)