title: Uppercases convert to lowercase when loading a file with h5py
body: <p>Hello I can't load a hdf5 file with h5py:</p>
  
  <pre><code>$ python verif.py 
  Traceback (most recent call last):
    File "verif.py", line 4, in &lt;module&gt;
      h5f = h5py.File("../DeepFISH-Github_projects/DeepFISH/dataset/'+'LowRes_13434_overlapping_pairs.h5",'r')
    File "/home/jeanpat/VirtualEnv/venv3/lib/python3.5/site-packages/h5py/_hl/files.py", line 272, in __init__
      fid = make_fid(name, mode, userblock_size, fapl, swmr=swmr)
    File "/home/jeanpat/VirtualEnv/venv3/lib/python3.5/site-packages/h5py/_hl/files.py", line 92, in make_fid
      fid = h5f.open(name, flags, fapl=fapl)
    File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper (/tmp/pip-at6d2npe-build/h5py/_objects.c:2684)
    File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper (/tmp/pip-at6d2npe-build/h5py/_objects.c:2642)
    File "h5py/h5f.pyx", line 76, in h5py.h5f.open (/tmp/pip-at6d2npe-build/h5py/h5f.c:1930)
  OSError: Unable to open file (Unable to open file: name = '../deepfish-github_projects/deepfish/dataset/'+'lowres_13434_overlapping_pairs.h5', errno = 2, error message = 'no such file or directory', flags = 0, o_flags = 0
  </code></pre>
  
  <p>The string containing the path to the file:</p>
  
  <pre><code>../DeepFISH-Github_projects/DeepFISH/dataset'+'LowRes_13434_overlapping_pairs.h5
  </code></pre>
  
  <p>seems to be modified by h5py</p>
  
  <pre><code> ../deepfish-github_projects/deepfish/dataset/lowres_13434_overlapping_pairs.h5
  </code></pre>
  
  <p>I could modify the directory name, but it's weird.</p>