Fix issue #23 with --no-ext-diff

Use `--no-ext-diff` to disable GIT_EXTERNAL_DIFF and diff.external which might
break cdiff output

CHANGES

 Change log
 ==========
 
+Version 0.9.1 (2013-05-20)
+
+  - Use `--no-ext-diff` to disable GIT_EXTERNAL_DIFF and diff.external which
+    might break cdiff output
+
 Version 0.9 (2013-03-23)
 
   - Supports reading context diff via ``filterdiff`` (patchutils)

cdiff.py

 """
 
 META_INFO = {
-    'version'     : '0.9',
+    'version'     : '0.9.1',
     'license'     : 'BSD-3',
     'author'      : 'Matthew Wang',
     'email'       : 'mattwyl(@)gmail(.)com',
 VCS_INFO = {
     'Git': {
         'probe' : ['git', 'rev-parse'],
-        'diff'  : ['env', '-u', 'GIT_EXTERNAL_DIFF', 'git', 'diff'],
+        'diff'  : ['git', 'diff', '--no-ext-diff'],
         'log'   : ['git', 'log', '--patch'],
     },
     'Mercurial': {