Modified revamp of the libsmbclient interface.

Modified revamp of the libsmbclient interface.

Given the tacit (if that) approval by some people, and clear disapproval by
others for my proposed clean-up and reorganization of libsmbclient, I've come
up with a slightly different approach.  This commit changes back to the
original libsmbclient.h SMBCCTX structure which will maintain ABI
compatibility.  I retain, here, the setter and getter functions which all new
code should use.  Older programs already compiled should continue to work
fine.  Older programs being recompiled will encounter compile-time errors
(intentionally!) so that the code can be corrected to use the setter/getter
interfaces.

Although this doesn't clean up the interface in the way I had wanted, the code
reorganization and requirement for new programs to use the setters and getters
allows future progress to be made on libsmbclient without further muddying up
the interface, while retaining the ABI compatibility that was the big issue
causing disapproval.  I hope that this compromise is adequate.

Derrell
(cherry picked from commit 56429a3d60b2a48963342f6340b3c01469a892c6)