don't close figures every cycle in inline backend

This allows gcf(), getfigs(), etc. to be useful again in the qtconsole and notebook.

draw_if_interactive() signals that the current figure is to be drawn.

Figures that are created and closed in the same cell will not be drawn.

See  #638

IPython/zmq/pylab/backend_inline.py

@@ -55,44 +55,67 b' class InlineBackendConfig(SingletonConfigurable):'
 # Functions
 #-----------------------------------------------------------------------------
 
-def show(close=True):
+def show(close=False):
     """Show all figures as SVG payloads sent to the IPython clients.
 
     Parameters
     ----------
     close : bool, optional
       If true, a ``plt.close('all')`` call is automatically issued after
-      sending all the SVG figures. If this is set, the figures will entirely
+      sending all the figures. If this is set, the figures will entirely
       removed from the internal list of figures.
     """
     for figure_manager in Gcf.get_all_fig_managers():
         send_figure(figure_manager.canvas.figure)
     if close:
         matplotlib.pyplot.close('all')
+    show._to_draw = []
+        
 
 
 # This flag will be reset by draw_if_interactive when called
 show._draw_called = False
+# list of figures to draw when flush_figures is called
+show._to_draw = []
 
 
 def draw_if_interactive():
     """
     Is called after every pylab drawing command
     """
-    # We simply flag we were called and otherwise do nothing.  At the end of
-    # the code execution, a separate call to show_close() will act upon this.
+    # signal that the current active figure should be sent at the end of execution.
+    # Also sets the _draw_called flag, signaling that there will be something to send.
+    # At the end of the code execution, a separate call to flush_figures()
+    # will act upon these values
+    
+    fig = Gcf.get_active().canvas.figure
+    
+    # ensure current figure will be drawn, and each subsequent call
+    # of draw_if_interactive() moves the active figure to ensure it is
+    # drawn last
+    try:
+        show._to_draw.remove(fig)
+    except ValueError:
+        # ensure it only appears in the draw list once
+        pass
+    show._to_draw.append(fig)
     show._draw_called = True
 
-
 def flush_figures():
-    """Call show, close all open figures, sending all figure images.
+    """Send all figures that changed
 
     This is meant to be called automatically and will call show() if, during
     prior code execution, there had been any calls to draw_if_interactive.
     """
-    if show._draw_called:
-        show()
-        show._draw_called = False
+    if not show._draw_called:
+        return
+    # exclude any figures that were closed:
+    active = set([fm.canvas.figure for fm in Gcf.get_all_fig_managers()])
+    for fig in [ fig for fig in show._to_draw if fig in active ]:
+        send_figure(fig)
+    # clear flags for next round
+    show._to_draw = []
+    show._draw_called = False
 
 
 def send_figure(fig):