Client lib: implement chunk and chunk access handling with chunk read state machine. Create chunk access class implementing chunk access request logic, and make it super class of all chunk server requests that access chunks, including read, write prepare, write sync, write append, write id alloc, size, and chunk space reservation. Replace KfsOp::Show() method that return string with the method that return op display wrapper to avoid string allocations, and use ostream insert operator directly. Create "null" client op to simplify handling of KfsOp null pointers in ostream insertion expressions.