testsuite: encoding error

[mlennert]

Whenever a test fails in the testsuite, and the LANGUAGE is fr_BE, I get the following error message

Traceback (most recent call last):
  File "test_r_mapcalc.py", line 99, in test_seed_required
    self.assertModuleFail('r.mapcalc', expression='rand_x = rand(1, 200)')
  File "/data/home/mlennert/SRC/GRASS/grass_trunk/dist.x86_64-pc-linux-gnu/etc/python/grass/gunittest/case.py", line 1180, in assertModuleFail
    module.run()
  File "/data/home/mlennert/SRC/GRASS/grass_trunk/dist.x86_64-pc-linux-gnu/etc/python/grass/pygrass/modules/interface/module.py", line 769, in run
    self.wait()
  File "/data/home/mlennert/SRC/GRASS/grass_trunk/dist.x86_64-pc-linux-gnu/etc/python/grass/pygrass/modules/interface/module.py", line 790, in wait
    module=self.name, errors=stderr)
  File "/data/home/mlennert/SRC/GRASS/grass_trunk/dist.x86_64-pc-linux-gnu/etc/python/grass/exceptions/__init__.py", line 71, in __init__
    msg += _(". See the following errors:\n%s") % errors
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 37: ordinal not in range(128)

[marisn]

Duplicate of #2875