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

Closes gh-1043

IPython/config/profile/pylab/ipython_config.py

@@ -8,7 +8,7 b" 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 *
@@ -20,4 +20,4 b' from matplotlib.pyplot import *'
 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]