Fix broken pens_updown_to_papr method (fix by @victoradan)

See https://github.com/drepetto/chiplotle/blob/13ac28a7645a018a4bc62980cb174627ca6b5b54/chiplotle/tools/hpgltools/pens_updown_to_papr.py

I lifted the code directly from there as the test looked to have been
originally broken, there is an open pull request to fix this issue on
the mainline at drepetto#5

chiplotle/tools/hpgltools/pens_updown_to_papr.py

@@ -1,5 +1,7 @@
+import copy
+
 from chiplotle.hpgl.commands import PA, PR, PU, PD
-from chiplotle.geometry.core.coordinate import Coordinate
+
 
 def pens_updown_to_papr(lst):
     '''Converts all PU((x1, y1, x2, y2) and PD(x1, y1, x2, y2) found in `lst`
@@ -11,63 +13,26 @@ def pens_updown_to_papr(lst):
         raise TypeError('`lst` argument must be a list or tuple.')
 
     result = [ ]
-    last_move = None
-
-    pen_down = False
-    pen_up = True
-
+    last_penplot = None
     for e in lst:
         if isinstance(e, (PU, PD)):
-
             if len(e.xy) > 0:
-                if last_move is None:
+                if last_penplot is None:
                     msg = "*** WARNING: %s with coordinates found without prior PA or PR. PA assumed." % e
                     print(msg)
-                    last_move = PA( )
-
-                new_move = None
-
-                if isinstance(last_move, PA):
-                    new_move = PA()
-                elif isinstance(last_move, PR):
-                    new_move = PR()
-
-                new_move.xy = e.xy
-
-                up_down_command = None
-
-                if isinstance(e, PU):
-                    if pen_down:
-                        up_down_command = PU( )
-                        result.append(up_down_command)
-                        pen_up = True
-                        pen_down = False
-
-                elif isinstance(e, PD):
-                    if pen_up:
-                        up_down_command = PD( )
-                        result.append(up_down_command)
-                        pen_down = True
-                        pen_up = False
-
-
-                result.append(new_move)
-
-                last_move = new_move
+                    last_penplot = PA( )
+                last_penplot.xy = e.xy
+                ec = copy.copy(e)
+                ec.xy = None
+                result.append(ec)
+                result.append(copy.copy(last_penplot))
             else:
-                if isinstance(e, PU):
-                    if pen_down:
-                        result.append(e)
-                        pen_up = True
-                elif isinstance(e, PD):
-                    if pen_up:
-                        result.append(e)
-                        pen_down = True
+                result.append(e)
         else:
             if isinstance(e, PR):
-                last_move = PR( )
+                last_penplot = PR( )
             elif isinstance(e, PA):
-                last_move = PA( )
+                last_penplot = PA( )
             result.append(e)
 
     return result