LibVNCClient: some users do not want to get whole-screen updates; introduce client->updateRect for that

rfbEncodingSupportedEncodings - What encodings are supported?
rfbEncodingSupportedMessages  - What message types are supported?
rfbEncodingServerIdentity     - What is the servers version string?
ie: "x11vnc: 0.8.1 lastmod: 2006-04-25 (LibVNCServer 0.9pre)"

We need to process the rectangle (especially if it a type that contains
subrectangles or any kind of compression).   UltraVNC should be fixed to
prevent these useless rectangles from being sent.

 fix deadlock from rfbReleaseExtensionIterator(), fix no libz/libjpeg builds, disable tightvnc-filetransfer if no libpthread, add --without-pthread option, rm // comments, set NAME_MAX if not defined, x11vnc: throttle load if fb update requests not taking place.

so that more than one data structure can be attached, and add an example
to speak the client part of the back channel.

Thank you very much, Rohit!

hide strict ansi stuff if not explicitely turned on; actually use the socklen_t test from configure.ac