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
define HEIMDAL_WARN_UNUSED_RESULT_ATTRIBUTE

Always define HEIMDAL_WARN_UNUSED_RESULT_ATTRIBUTE even if attributes are
not supported.

Change-Id: Ibc2110d809d81f546723853038c69176075d6013
improve resolve_origin readability

comment the HAVE_DLADDR preprocessor #else and #endif
because they are so many lines apart.

indent the strrchr() call after the _Win32 block to demonstrate
they are related.

Change-Id: I112dc91b350b277cdb1dc1cd3ccd8f31a2084409
min instead of MIN

The MIN macro is not defined everywhere.  use min().

Change-Id: I47413080364e215ad2a2075403b224867deba037
Windows packaging: install kadmin.exe

Now that kadmin.exe works on Windows, install it.

Change-Id: I4b5e85386bd6e39ac1a8e01cd6d323c09520da1a