title: matplotlib pgf savefig(pdf) fails
body: <p>On a modern texlive installation on fedora 20, using pgf backend fails in savefig ('blah.pdf'). </p>
  
  <p>Example:</p>
  
  <pre><code># -*- coding: utf-8 -*-
  
  import matplotlib as mpl
  mpl.use("pgf")
  pgf_with_rc_fonts = {
      "font.family": "serif",
      "font.serif": [],                   # use latex default serif font
      "font.sans-serif": ["DejaVu Sans"], # use a specific sans-serif font
  }
  mpl.rcParams.update(pgf_with_rc_fonts)
  
  import matplotlib.pyplot as plt
  plt.figure(figsize=(4.5,2.5))
  plt.plot(range(5))
  plt.text(0.5, 3., "serif")
  plt.text(0.5, 2., "monospace", family="monospace")
  plt.text(2.5, 2., "sans-serif", family="sans-serif")
  plt.text(2.5, 1., "comic sans", family="Comic Sans MS")
  plt.xlabel(u"µ is not $\\mu$")
  plt.tight_layout(.5)
  </code></pre>
  
  <p>trace back:</p>
  
  <pre><code>Traceback (most recent call last):
    File "testpgf.py", line 20, in &lt;module&gt;
      plt.tight_layout(.5)
    File "/usr/lib64/python2.7/site-packages/matplotlib/pyplot.py", line 1255, in tight_layout
      fig.tight_layout(pad=pad, h_pad=h_pad, w_pad=w_pad, rect=rect)
    File "/usr/lib64/python2.7/site-packages/matplotlib/figure.py", line 1600, in tight_layout
      renderer = get_renderer(self)
    File "/usr/lib64/python2.7/site-packages/matplotlib/tight_layout.py", line 222, in get_renderer
      renderer = canvas.get_renderer()
    File "/usr/lib64/python2.7/site-packages/matplotlib/backends/backend_pgf.py", line 925, in get_renderer
      return RendererPgf(self.figure, None, dummy=True)
    File "/usr/lib64/python2.7/site-packages/matplotlib/backends/backend_pgf.py", line 409, in __init__
      self.latexManager = LatexManagerFactory.get_latex_manager()
    File "/usr/lib64/python2.7/site-packages/matplotlib/backends/backend_pgf.py", line 223, in get_latex_manager
      new_inst = LatexManager()
    File "/usr/lib64/python2.7/site-packages/matplotlib/backends/backend_pgf.py", line 305, in __init__
      cwd=self.tmpdir)
    File "/usr/lib64/python2.7/subprocess.py", line 711, in __init__
      errread, errwrite)
    File "/usr/lib64/python2.7/subprocess.py", line 1308, in _execute_child
      raise child_exception
  OSError: [Errno 2] No such file or directory
  </code></pre>