Bug in postscript backend in Python 3

The following examples demonstrates the issue:

```
In [1]: import matplotlib

In [2]: matplotlib.__version__
Out[2]: '1.2.0'

In [3]: from matplotlib import pyplot as plt

In [4]: fig = plt.figure()

In [5]: ax = fig.add_subplot(1,1,1)

In [6]: import numpy as np

In [7]: ax.imshow(np.zeros((128, 128)))
Out[7]: <matplotlib.image.AxesImage at 0x105085ed0>

In [8]: fig.savefig('test.ps')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-8-d877e517da66> in <module>()
----> 1 fig.savefig('test.ps')

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/figure.py in savefig(self, *args, **kwargs)
   1362             kwargs.setdefault('edgecolor', rcParams['savefig.edgecolor'])
   1363 
-> 1364         self.canvas.print_figure(*args, **kwargs)
   1365 
   1366         if transparent:

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, **kwargs)
   2091                 orientation=orientation,
   2092                 bbox_inches_restore=_bbox_inches_restore,
-> 2093                 **kwargs)
   2094         finally:
   2095             if bbox_inches and restore_bbox:

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/backend_bases.py in print_ps(self, *args, **kwargs)
   1858         from .backends.backend_ps import FigureCanvasPS # lazy import
   1859         ps = self.switch_backends(FigureCanvasPS)
-> 1860         return ps.print_ps(*args, **kwargs)
   1861 
   1862     def print_raw(self, *args, **kwargs):

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/backends/backend_ps.py in print_ps(self, outfile, *args, **kwargs)
    969 
    970     def print_ps(self, outfile, *args, **kwargs):
--> 971         return self._print_ps(outfile, 'ps', *args, **kwargs)
    972 
    973     def print_eps(self, outfile, *args, **kwargs):

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/backends/backend_ps.py in _print_ps(self, outfile, format, *args, **kwargs)
   1005             self._print_figure(outfile, format, imagedpi, facecolor, edgecolor,
   1006                                orientation, isLandscape, papertype,
-> 1007                                **kwargs)
   1008 
   1009     def _print_figure(self, outfile, format, dpi=72, facecolor='w', edgecolor='w',

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/backends/backend_ps.py in _print_figure(self, outfile, format, dpi, facecolor, edgecolor, orientation, isLandscape, papertype, **kwargs)
   1098             bbox_inches_restore=_bbox_inches_restore)
   1099 
-> 1100         self.figure.draw(renderer)
   1101 
   1102         if dryrun: # return immediately if dryrun (tightbbox=True)

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     53     def draw_wrapper(artist, renderer, *args, **kwargs):
     54         before(artist, renderer)
---> 55         draw(artist, renderer, *args, **kwargs)
     56         after(artist, renderer)
     57 

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/figure.py in draw(self, renderer)
    998         dsu.sort(key=itemgetter(0))
    999         for zorder, a, func, args in dsu:
-> 1000             func(*args)
   1001 
   1002         renderer.close_group('figure')

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     53     def draw_wrapper(artist, renderer, *args, **kwargs):
     54         before(artist, renderer)
---> 55         draw(artist, renderer, *args, **kwargs)
     56         after(artist, renderer)
     57 

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/axes.py in draw(self, renderer, inframe)
   2086 
   2087         for zorder, a in dsu:
-> 2088             a.draw(renderer)
   2089 
   2090         renderer.close_group('axes')

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     53     def draw_wrapper(artist, renderer, *args, **kwargs):
     54         before(artist, renderer)
---> 55         draw(artist, renderer, *args, **kwargs)
     56         after(artist, renderer)
     57 

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/image.py in draw(self, renderer, *args, **kwargs)
    364             im._url = self.get_url()
    365             im._gid = self.get_gid()
--> 366             renderer.draw_image(gc, l, b, im)
    367         gc.restore()
    368 

/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/matplotlib/backends/backend_ps.py in draw_image(self, gc, x, y, im, dx, dy, transform)
    470 
    471         h, w, bits, imagecmd = self._get_image_h_w_bits_command(im)
--> 472         hexlines = '\n'.join(self._hex_lines(bits))
    473 
    474         if dx is None:

TypeError: sequence item 0: expected str instance, bytes found
```

In the mean time, is there a workaround?