Fixed inferring the base name.

IPython/nbformat/v2/__init__.py

@@ -74,6 +74,7 b' def parse_filename(fname):'
     elif ext == u'.py':
         format = u'py'
     else:
+        basename = fname
         fname = fname + u'.ipynb'
         format = u'json'
     return fname, basename, format

IPython/nbformat/v3/__init__.py

@@ -71,6 +71,7 b' def parse_filename(fname):'
     elif ext == u'.py':
         format = u'py'
     else:
+        basename = fname
         fname = fname + u'.ipynb'
         format = u'json'
     return fname, basename, format