Rename most of the platform source files.

This gets rid of all those annoying 'win', 'ux' and 'gtk' prefixes
which made filenames annoying to type and to tab-complete. Also, as
with my other recent renaming sprees, I've taken the opportunity to
expand and clarify some of the names so that they're not such cryptic
abbreviations.

unix/pterm.c

@@ -0,0 +1,50 @@
+/*
+ * pterm main program.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "putty.h"
+
+const char *const appname = "pterm";
+const bool use_event_log = false;      /* pterm doesn't need it */
+const bool new_session = false, saved_sessions = false; /* or these */
+const bool dup_check_launchable = false; /* no need to check host name
+                                          * in conf */
+const bool use_pty_argv = true;
+
+const unsigned cmdline_tooltype = TOOLTYPE_NONNETWORK;
+
+/* gtkwin.c will call this, and in pterm it's not needed */
+void noise_ultralight(NoiseSourceId id, unsigned long data) { }
+
+const struct BackendVtable *select_backend(Conf *conf)
+{
+    return &pty_backend;
+}
+
+void initial_config_box(Conf *conf, post_dialog_fn_t after, void *afterctx)
+{
+    /*
+     * This is a no-op in pterm, except that we'll ensure the protocol
+     * is set to -1 to inhibit the useless Connection panel in the
+     * config box. So we do that and then just immediately call the
+     * post-dialog function with a positive result.
+     */
+    conf_set_int(conf, CONF_protocol, -1);
+    after(afterctx, 1);
+}
+
+void cleanup_exit(int code)
+{
+    exit(code);
+}
+
+void setup(bool single)
+{
+    settings_set_default_protocol(-1);
+
+    if (single)
+        pty_pre_init();
+}