Revision 1656488

Introduce a private libsvn_client context structure that stores
context information that should not be part of the public API.

* subversion/include/svn_client.h
  (svn_client_ctx_t): Remove the 'progress' field, which should be private.

* subversion/libsvn_client/client.h
  (client_ctx_t): New; the private context struct.
   Contains the equivalent of the 'progress' field.
  (svn_client__get_private_ctx): New prototype.
* subversion/libsvn_client/ctx.c: Include stddef.h and client.h.
  (CLIENT_CTX_MAGIC): New; magic number for the private context.
  (svn_client__get_private_ctx): Implement.
  (svn_client_create_context2): Allocate and initialize the private
   context structure, with the public context embedded within it.
* subversion/libsvn_client/ra.c
  (progress_func): Use the total progress counter from the private context.