Installing mayavi does not downgrade all necessary packages

[larsoner]

On linux, I install latest numpy + h5py (plus some other packages):

numpy-1.10.4               |           py27_0         6.0 MB
...
h5py-2.5.0                 |      np110py27_4         2.4 MB

But then in another command tell it to install mayavi:

mayavi-4.4.0               |       np19py27_0        10.3 MB

And it goes to downgrade, but does not downgrade h5py:

The following packages will be DOWNGRADED:

    matplotlib: 1.5.1-np110py27_0  --> 1.4.3-np19py27_2 
    numpy:      1.10.4-py27_0      --> 1.9.3-py27_0     
    scipy:      0.17.0-np110py27_1 --> 0.16.0-np19py27_1

So then on import of h5py I get:

  File "/home/travis/miniconda/envs/testenv/lib/python2.7/site-packages/h5py/__init__.py", line 23, in <module>
    from . import _conv
  File "h5py/h5t.pxd", line 14, in init h5py._conv (/home/ilan/minonda/conda-bld/work/h5py/_conv.c:7364)
  File "h5py/numpy.pxd", line 66, in init h5py.h5t (/home/ilan/minonda/conda-bld/work/h5py/h5t.c:20460)
ValueError: numpy.dtype has the wrong size, try recompiling

If a full set of conda commands is necessary to reproduce, I can get it.

[larsoner]

Possible / likely dup of #486, feel free to close if so

[larsoner]

If anybody has time to outline roughly what needs to be changed to fix this sort of issue (files to change, etc.), I'm happy to take a stab at it