Move some parts of window.c into putty.c.

This prepares the ground for a second essentially similarly-shaped
program reusing most of window.c but handling its command line and
startup differently. A couple of large parts of WinMain() to do with
backend selection and command-line handling are now subfunctions in a
separate file putty.c.

Also, our custom AppUserModelId is defined in that file, so that it
can vary with the client application.

windows/putty.c

@@ -0,0 +1,127 @@
+#include "putty.h"
+#include "storage.h"
+
+void gui_term_process_cmdline(Conf *conf, char *cmdline)
+{
+    char *p;
+    bool special_launchable_argument = false;
+
+    settings_set_default_protocol(be_default_protocol);
+    /* Find the appropriate default port. */
+    {
+        const struct BackendVtable *vt =
+            backend_vt_from_proto(be_default_protocol);
+        settings_set_default_port(0); /* illegal */
+        if (vt)
+            settings_set_default_port(vt->default_port);
+    }
+    conf_set_int(conf, CONF_logtype, LGTYP_NONE);
+
+    do_defaults(NULL, conf);
+
+    p = handle_restrict_acl_cmdline_prefix(cmdline);
+
+    if (handle_special_sessionname_cmdline(p, conf)) {
+        if (!conf_launchable(conf) && !do_config(conf)) {
+            cleanup_exit(0);
+        }
+        special_launchable_argument = true;
+    } else if (handle_special_filemapping_cmdline(p, conf)) {
+        special_launchable_argument = true;
+    } else if (!*p) {
+        /* Do-nothing case for an empty command line - or rather,
+         * for a command line that's empty _after_ we strip off
+         * the &R prefix. */
+    } else {
+        /*
+         * Otherwise, break up the command line and deal with
+         * it sensibly.
+         */
+        int argc, i;
+        char **argv;
+
+        split_into_argv(cmdline, &argc, &argv, NULL);
+
+        for (i = 0; i < argc; i++) {
+            char *p = argv[i];
+            int ret;
+
+            ret = cmdline_process_param(p, i+1<argc?argv[i+1]:NULL,
+                                        1, conf);
+            if (ret == -2) {
+                cmdline_error("option \"%s\" requires an argument", p);
+            } else if (ret == 2) {
+                i++;               /* skip next argument */
+            } else if (ret == 1) {
+                continue;          /* nothing further needs doing */
+            } else if (!strcmp(p, "-cleanup")) {
+                /*
+                 * `putty -cleanup'. Remove all registry
+                 * entries associated with PuTTY, and also find
+                 * and delete the random seed file.
+                 */
+                char *s1, *s2;
+                s1 = dupprintf("This procedure will remove ALL Registry entries\n"
+                               "associated with %s, and will also remove\n"
+                               "the random seed file. (This only affects the\n"
+                               "currently logged-in user.)\n"
+                               "\n"
+                               "THIS PROCESS WILL DESTROY YOUR SAVED SESSIONS.\n"
+                               "Are you really sure you want to continue?",
+                               appname);
+                s2 = dupprintf("%s Warning", appname);
+                if (message_box(NULL, s1, s2,
+                                MB_YESNO | MB_ICONWARNING | MB_DEFBUTTON2,
+                                HELPCTXID(option_cleanup)) == IDYES) {
+                    cleanup_all();
+                }
+                sfree(s1);
+                sfree(s2);
+                exit(0);
+            } else if (!strcmp(p, "-pgpfp")) {
+                pgp_fingerprints_msgbox(NULL);
+                exit(1);
+            } else if (*p != '-') {
+                cmdline_error("unexpected argument \"%s\"", p);
+            } else {
+                cmdline_error("unknown option \"%s\"", p);
+            }
+        }
+    }
+
+    cmdline_run_saved(conf);
+
+    /*
+     * Bring up the config dialog if the command line hasn't
+     * (explicitly) specified a launchable configuration.
+     */
+    if (!(special_launchable_argument || cmdline_host_ok(conf))) {
+        if (!do_config(conf))
+            cleanup_exit(0);
+    }
+
+    prepare_session(conf);
+}
+
+const struct BackendVtable *backend_vt_from_conf(Conf *conf)
+{
+    /*
+     * Select protocol. This is farmed out into a table in a
+     * separate file to enable an ssh-free variant.
+     */
+    const struct BackendVtable *vt = backend_vt_from_proto(
+        conf_get_int(conf, CONF_protocol));
+    if (!vt) {
+        char *str = dupprintf("%s Internal Error", appname);
+        MessageBox(NULL, "Unsupported protocol number found",
+                   str, MB_OK | MB_ICONEXCLAMATION);
+        sfree(str);
+        cleanup_exit(1);
+    }
+    return vt;
+}
+
+const wchar_t *get_app_user_model_id(void)
+{
+    return L"SimonTatham.PuTTY";
+}