creates index in new h5 file even when it wasn't successfully created

Issue:

when you try and create a node on the omx and it doesn't do so successfully, it doesn't delete the node. Need to make it fail gracefully and delete if it doesn't finish creating.

Traceback:

>>> outFile["test1"]=m1in
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "omx\File.py", line 178, in __setitem__
    return self.createMatrix(key, atom, shape, obj=dataset)
  File "omx\File.py", line 33, in createMatrix
    chunkshape, byteorder, createparents)
  File "C:\Python27\Lib\site-packages\tables\file.py", line 831, in createCArray

    chunkshape=chunkshape, byteorder=byteorder)
  File "C:\Python27\Lib\site-packages\tables\carray.py", line 203, in __init__
    byteorder, _log)
  File "C:\Python27\Lib\site-packages\tables\leaf.py", line 263, in __init__
    super(Leaf, self).__init__(parentNode, name, _log)
  File "C:\Python27\Lib\site-packages\tables\node.py", line 241, in __init__
    parentNode._g_refNode(self, name, validate)
  File "C:\Python27\Lib\site-packages\tables\group.py", line 494, in _g_refNode
    % (self._v_pathname, childName))
tables.exceptions.NodeError: group ``/`` already has a child node named ``test1`

osPlanning / omx

creates index in new h5 file even when it wasn't successfully created #7