DWDS/Dialing Concordance Code

+ threadme2 test working with DDCThread wrapper class

+ CHost/string_socket refactorization cleanup
- moved old CHost::AnswerByRequest() calling context in RunThread() into virtual HandleClientConnection() [thread magic to happen here later]
- moved old CHost::AnswerByRequest() to CHost::HandleClientRequest(): handle a single client request [should be thread-local]
- factored HandleClientRequest() into GetRequest(), SendResponse(), and HandleSocketError()
- report client peer address with CHost errors using new SocketPeer() function [doesn't work for closed sockets of course]

+ factored CHost class out of string_socket.(h|cpp)

+ more threadme tests

+ added DDCThread.(cpp|h), adapted from https://vichargrave.github.io/articles/2012-12/java-style-thread-class-in-cpp

+ on-demand thread creation working; TODO: pre-allocate?

+ merged more ddc-v2.0.52 changes into threaded-server branch ( svn+ssh://mukau@.../p/ddc-concordance/code/ddc/trunk -r738:742 . )

+ tagged ddc-2.0.52

+ removed bogus tag ddc-2.0.52

+ changed filter-copying wonk-up with v2.0.52