Setting font type using rcParams does not work under Python 3.*

The following code:
```python
import matplotlib as mpl
import matplotlib.pyplot as plt
# if I omit the next line, the plot saves without error, but with outlined fonts
mpl.rcParams['pdf.fonttype'] = 42        #set Truetype fonts for Adobe
plt.plot(range(5),range(5),'r-')
plt.ylabel('y')
plt.xlabel('x')
plt.title('title')
plt.savefig("myfig.pdf")
```
runs fine in Python 2.7.3, but causes `TypeError: 'str' does not support the buffer interface` error in Python 3.3 on OsX and Python 3.2.3 on Linux.

(se also http://stackoverflow.com/questions/16391280/python-3-3-matplotlib-1-2-0-pdf-export-generates-str-does-not-support-the )