Use qt4agg, not qtagg, mpl backend in pylab profile.

Closes gh-1043

IPython/config/profile/pylab/ipython_config.py

@@ -1,23 +1,23 b''
 c = get_config()
 app = c.InteractiveShellApp
 
 # This can be used at any point in a config file to load a sub config
 # and merge it into the current one.
 load_subconfig('ipython_config.py', profile='default')
 
 lines = """
 import matplotlib
 %gui qt
-matplotlib.use('qtagg')
+matplotlib.use('qt4agg')
 matplotlib.interactive(True)
 from matplotlib import pyplot as plt
 from matplotlib.pyplot import *
 """
 
 # You have to make sure that attributes that are containers already
 # exist before using them.  Simple assigning a new list will override
 # all previous values.
 if hasattr(app, 'exec_lines'):
     app.exec_lines.append(lines)
 else:
-    app.exec_lines = [lines]
  No newline at end of file
+    app.exec_lines = [lines]