[Reviewer Matt] Remove special case handling of 1xx responses on forked transactions

Matt

A fix for the issue with odd handling of 1xx responses on forked transactions.  There's some spurious white-space differences in the diff, which are probably down to my editor settings - sorry).  The fix basically involves removing some special case code we added right at the beginning of Clearwater development (before it was called Clearwater) to get around some issues with clients that didn't seem to like being downstream of a forking proxy.  This isn't relevant any more, so it should be safe to remove this code.

I've tested by fixing up the unit tests that were checking for this.  They aren't 100% perfect as they don't check that the To: tags are propagated properly, but I couldn't see how to easily do this check and wanted to get the fix out today.

Mike