When giving authorisation errors from the proxy code in x11fwd.c,

name the proxy using the global 'appname' variable, instead of
statically calling it PuTTY.

(Knock-on effect is that PSCP and PSFTP have to declare that
variable, though of course they shouldn't ever actually _use_ the X
forwarding code. Probably I ought to replace it with a stub
nox11fwd.c for those applications.)

[originally from svn r8501]

psftp.c

@@ -16,6 +16,8 @@
 #include "sftp.h"
 #include "int64.h"
 
+const char *const appname = "PSFTP";
+
 /*
  * Since SFTP is a request-response oriented protocol, it requires
  * no buffer management: when we send data, we stop and wait for an