Libdap refactor

libdap code/features to remove

In DODSFilter
- Remove 'COMPRESSION_FOR_SERVER3' code
- Remove the FILE* methods - this will break some of the older 'cgi handlers' but those should be removed anyway
- CGI processing code in general - how much of this is being used at all?
- read_ancillary_das() methods - replace with direct calls to Ancillary?
- Look at the DODSFilter unit tests to make sure that some of the CGI code is not used there.
cgi-util.cc
- Remove the FILE* functions and/or replace with ostream ones if those are not already there.
AIS - remove completely
XDRFileMarshaller - We can remove this
XDRFileUnMarshaller - We can remove this once we have an XDRStreamUnMarshaller and...
Look at Response, HTTPResponse, and see how they use FILE*. Can this be changes to an ostream easily. More of a refactor...

We need a XDRStreamUnMarshaller - this will let me remove lots of the FILE* code.
Change HTTPConnect so that it works with data in memory when possible