Fixed instances of 'from pytest import something'. For the most part this meant doing 'from ...tests.helper import pytest' and then changing 'something' to 'pytest.something'.
Fixed a hanging 'misc' left in after merging test_pickle_helpers.py.
And fix importing test.helper from the wrong level after move of test_pickle_helpers.py.
minor typo fix in stats.funcs
Merge pull request #454 from iguananaut/fix-system-pytest

Check for '_pytest' in sys.modules before trying to import Astropy's pytest
fixed problem with clearing cache screwing up lock.  Closes #480
added lock/pid file to report which pid placed the cache lock
changed cache directory name to "download" to reflect wider scope
add tests for all examples in API document
import quantity into units/__init__
initial implementation of Quantity object
fill out docstrings a bit more
fix string formatting bracket ambiguity
fix number -> string formatting bug
added _repr_latex_ to Quantity for ipython notebook
Add exponential notation to LaTeX representation of quantities
Change ValueError to TypeError and add validation function for value
Add value attribute and update docstrings
remove radd, rsub, update rmul and rdiv to allow arithmetic with numbers
add tests for arithmetic with numbers