ssh: Add support for Putty.

* agent/gpg-agent.c [W32]: Include Several Windows header.
(opts): Change help text for enable-ssh-support.
(opts, main): Add option --enable-putty-support
(putty_support, PUTTY_IPC_MAGIC, PUTTY_IPC_MAXLEN): New for W32.
(agent_init_default_ctrl): Add and asssert call.
(putty_message_proc, putty_message_thread): New.
(handle_connections) [W32]: Start putty message thread.
* common/sysutils.c (w32_get_user_sid): New for W32 only
* tools/gpgconf-comp.c (gc_options_gpg_agent): Add
--enable-ssh-support and --enable-putty-support.  Make the
configuration group visible at basic level.
* agent/command-ssh.c (serve_mmapped_ssh_request): New for W32 only.
--

This patch enables support for Putty.  It has been tested with Putty
0.62 using an Unix created ssh key copied to the private-keys-v1.d
directory on Windows and with a manually crafted sshcontrol file.  It
also works with a smartcard key.

May thanks to gniibe who implemented a proxy in Python to test the
putty/gpg-agent communication.

Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit 9f32499f99)

Resolved conflicts:
	NEWS
	agent/agent.h
	agent/gpg-agent.c: Convert from pth to npth.
	common/sysutils.c
	common/sysutils.h

common/sysutils.h

@@ -65,6 +65,7 @@ int  gnupg_setenv (const char *name, const char *value, int overwrite);
 int  gnupg_unsetenv (const char *name);
 
 #ifdef HAVE_W32_SYSTEM
+void *w32_get_user_sid (void);
 
 #include "../common/w32help.h"