First phase of porting. pterm now compiles and runs under Linux+gtk.

The current pty.c backend is temporarily a loopback device for
terminal emulator testing, the display handling is only just enough
to show that terminal.c is functioning, the keyboard handling is
laughable, and most features are absent. Next step: bring output and
input up to a plausibly working state, and put a real pty on the
back to create a vaguely usable prototype. Oh, and a scrollbar would
be nice too.
In _theory_ the Windows builds should still work fine after this...

[originally from svn r2010]

unix/uxprint.c

@@ -0,0 +1,24 @@
+/*
+ * Printing interface for PuTTY.
+ */
+
+#include <assert.h>
+#include "putty.h"
+
+printer_job *printer_start_job(char *printer)
+{
+    /* FIXME: open pipe to lpr */
+    return NULL;
+}
+
+void printer_job_data(printer_job *pj, void *data, int len)
+{
+    /* FIXME: receive a pipe to lpr, write things to it */
+    assert(!"We shouldn't get here");
+}
+
+void printer_finish_job(printer_job *pj)
+{
+    /* FIXME: receive a pipe to lpr, close it */
+    assert(!"We shouldn't get here either");
+}