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/printing.c

@@ -0,0 +1,58 @@
+/*
+ * Printing interface for PuTTY.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include "putty.h"
+
+struct printer_job_tag {
+    FILE *fp;
+};
+
+printer_job *printer_start_job(char *printer)
+{
+    printer_job *ret = snew(printer_job);
+    /*
+     * On Unix, we treat the printer string as the name of a
+     * command to pipe to - typically lpr, of course.
+     */
+    ret->fp = popen(printer, "w");
+    if (!ret->fp) {
+        sfree(ret);
+        ret = NULL;
+    }
+    return ret;
+}
+
+void printer_job_data(printer_job *pj, const void *data, size_t len)
+{
+    if (!pj)
+        return;
+
+    if (fwrite(data, 1, len, pj->fp) < len)
+        /* ignore */;
+}
+
+void printer_finish_job(printer_job *pj)
+{
+    if (!pj)
+        return;
+
+    pclose(pj->fp);
+    sfree(pj);
+}
+
+/*
+ * There's no sensible way to enumerate printers under Unix, since
+ * practically any valid Unix command is a valid printer :-) So
+ * these are useless stub functions, and uxcfg.c will disable the
+ * drop-down list in the printer configurer.
+ */
+printer_enum *printer_start_enum(int *nprinters_ptr) {
+    *nprinters_ptr = 0;
+    return NULL;
+}
+char *printer_get_name(printer_enum *pe, int i) { return NULL;
+}
+void printer_finish_enum(printer_enum *pe) { }