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.

windows/psocks.c

@@ -0,0 +1,24 @@
+/*
+ * Main program for Windows psocks.
+ */
+
+#include "putty.h"
+#include "ssh.h"
+#include "psocks.h"
+
+static const PsocksPlatform platform = {
+    NULL /* open_pipes */,
+    NULL /* start_subcommand */,
+};
+
+int main(int argc, char **argv)
+{
+    psocks_state *ps = psocks_new(&platform);
+    psocks_cmdline(ps, argc, argv);
+
+    sk_init();
+    winselcli_setup();
+    psocks_start(ps);
+
+    cli_main_loop(cliloop_null_pre, cliloop_null_post, NULL);
+}