I'm pretty sure it doesn't work. ```find_tag``` is weird it seems to only work on ```tree``` nodes (I still can't figure out what these are). I was thinking about renaming find_tag to be find_tag_node and maybe adding find_tag_dir.

Example
----------
```
import mne
from mne.fiff import FIFF
fid, tree, directory = mne.fiff.fiff_open('examples/MNE-sample-data/MEG/sample/sample_audvis_raw-trans.fif')
tag = mne.fiff.tag.find_tag(fid, directory, FIFF.FIFF_COORD_TRANS)
TypeError                                 Traceback (most recent call last)
<ipython-input-8-5a96dd321b05> in <module>()
----> 1 tag = mne.fiff.tag.find_tag(fid, directory, FIFF.FIFF_COORD_TRANS)

/autofs/cluster/neuromind/dwakeman/mne-python/mne/fiff/tag.pyc in find_tag(fid, node, findkind)
    472     """Find Tag in an open FIF file descriptor
    473     """
--> 474     for p in range(node['nent']):
    475         if node['directory'][p].kind == findkind:
    476             return read_tag(fid, node['directory'][p].pos)

TypeError: list indices must be integers, not str
```