RF: revert fix allowing upper case file extensions

I thought about this for a while, but I don't like it, because it
changes the behavior of nibabel globally. Previously if you asked to
open ``my_image.NII`` it would barf, now it might find an image when it
previously it did not.  This is probably what the user intended, but
it's still a guess.  It's not hard to specify the upper case file
extension on systems that need it.

The next commit adds an explicit function to ignore extension case for
parrec2nii.

Author: matthew-brett

nibabel/openers.py

@@ -9,7 +9,7 @@
 """ Context manager openers for various fileobject types
 """
 
-from os.path import splitext, isfile
+from os.path import splitext
 import gzip
 import bz2
 
@@ -49,10 +49,6 @@ def __init__(self, fileish, *args, **kwargs):
             self._name = None
             return
         _, ext = splitext(fileish)
-        # allow for ext to be lower or upper case
-        if not isfile(fileish):
-            if isfile(_ + ext.upper()):
-                fileish = _ + ext.upper()
         if ext in self.compress_ext_map:
             is_compressor = True
             opener, arg_names = self.compress_ext_map[ext]