python core backtraces miss str(ex) for ImportError

[jfilak]

https://retrace.fedoraproject.org/faf/reports/234340/
http://ubuntuforums.org/archive/index.php/t-1849993.html

Traceback (most recent call last):
File "/usr/lib/gimp/2.0/plug-ins/text-brush.py", line 20, in <module>
from gimpfu import *
File "/usr/lib/gimp/2.0/python/gimpfu.py", line 76, in <module>
import gimp
ImportError: /usr/lib/gimp/2.0/python/gimp.so: undefined symbol: PyGimpItem_Type