[with patch, positive review] R.py doctest fails for non-english locale

[GeorgSWeber]

Testing Sage-4.1.2-alpha4, I saw that the old failure from #6379 somehow was resurrected (probably by using some new version of the R package that has changed its internationalized warning messages). To reproduce the failure, do something (or nothing, see also #6379) like

export LANG=de_DE.UTF-8

from a (sage -sh) shell and then you'll get:

sage -t -long "devel/sage/sage/interfaces/r.py"             
**********************************************************************
File "/Users/Shared/sage/sage-4.1.2.alpha4/devel/sage/sage/interfaces/r.py", line 549:
    sage: r.library('foobar')
Expected:
    Traceback (most recent call last):
    ...
    ImportError: ...
Got nothing
**********************************************************************
File "/Users/Shared/sage/sage-4.1.2.alpha4/devel/sage/sage/interfaces/r.py", line 839:
    sage: r.completions('tes')
Expected:
    ['testInheritedMethods', 'testPlatformEquivalence', 'testVirtual']
Got:
    ['testInheritedMethods', 'testInheritedMethods', 'testPlatformEquivalence', 'testPlatformEquivalence', 'testVirtual', 'testVirtual']
**********************************************************************
2 items had failures:
   1 of   5 in __main__.example_17
   1 of   4 in __main__.example_34
***Test Failed*** 2 failures.
For whitespace errors, see the file /Users/georgweber/.sage//tmp/.doctest_r.py
         [7.3 s]
exit code: 1024
 
----------------------------------------------------------------------
The following tests failed:


        sage -t -long "devel/sage/sage/interfaces/r.py"

Fortunately, I fiddled around with this file and this bug more than once (see also #6594, #6646), so I knew where to look. Hopefully, this zombie is put down to rest ...

[GeorgSWeber]

tested against 4.1.2.alpha4

[was]

merged in sage-4.1.2.rc1...