Return zero when reporting our version.

When called with -V to ask for our version, return 0 rather than 1.
This is the usual behaviour observed by ssh(1) and other Unix commands.
Also use exit() rather than cleanup_exit() in pscp.c and psftp.c ; at
this point we have nothing to cleanup!

pscp.c

@@ -2272,7 +2272,7 @@ void version(void)
     char *buildinfo_text = buildinfo("\n");
     printf("pscp: %s\n%s\n", ver, buildinfo_text);
     sfree(buildinfo_text);
-    cleanup_exit(1);
+    exit(0);
 }
 
 void cmdline_error(const char *p, ...)