Introduce and apply krb5_storage_from_socket

On Windows a file descriptor is an int value allocated by the
local module instance of the C Run Time Library.  A socket handle is a
SOCKET value allocated by a Winsock Provider for the requested family and
protocol.   These two values cannot be mixed and there is no mechanism for
converting between the two.   The _get_osfhandle() and _open_osfhandle()
functions can work with a standard HANDLE (file, pipe, etc) but cannot be
used for a SOCKET.

The Heimdal krb5_storage_from_fd() routine counted on the osf conversion
functions working on SOCKET values.  Since they do not any attempt to call
krb5_storage_from_fd() on a socket resulted in an assertion being thrown
by the C RTL.

Another problem is SOCKET value truncation when storing a 64-bit value
into a 32-bit int.

To address these problems a new krb5_storage_from_socket() routine is
introduced.  This routine setups a krb5_storage that stores a socket value
as a rk_socket_t and provides a set of helper routines that always use
network ready functions.

The krb5_storage_from_fd() routines no longer use net_read() and
net_write() but provide helpers that follow their logic so that pipes can
be processed.

All call sites that allocate a socket now store the socket as rk_socket_t
and call krb5_storage_from_socket().

All locations that previously called the bare close() on a socket value
now call rk_closesocket().

Change-Id: I045f775b2a5dbf5cf803751409490bc27fffe597

kadmin/rpc.c

@@ -1097,7 +1097,7 @@ handle_mit(krb5_context contextp, void *buf, size_t len, krb5_socket_t sock)
 
     dcontext = contextp;
 
-    sp = krb5_storage_from_fd(sock);
+    sp = krb5_storage_from_socket(sock);
     INSIST(sp != NULL);
 
     process_stream(contextp, buf, len, sp);