TST : fail sensibly on py3k

Fail sensible in py3k for c-extension related tests.

Use the `known_fail_if` decorator to fail the ctrans related
tests if we are under python 3
MNT : simplified process_to_q test

Simplified code in test to allow easy extension to testing more points.
TST : Added more tests to test_recip

Uses test that has one point in the center of each grid.
Now checks that all points are in grid, the occupancy is correct, and
that intensity array is exactly equal.
TST : added second test to test error

Added second test of gridder
ENH : made exceptions have useful messages

Now tell the user what the ValueError is (shape of input data)
DOC : corrected documentation of gridder

the error value is actually the standard error, not the standard
deviation.

Made other docs more verbose
ENH: Added binary_mask as input parameter for grid3d

This is the a mechanism that I came up with for masking
bad regions of images that I think @tacaswell will agree with.
The other approach would require masking before process_to_q.  If
we go down that route, then process_to_q will need to take in the
image stack again.
MNT: binary mask application to q is working, thanks @tacaswell
MNT: More memory efficient binary_mask creation
MNT: Binary mask needed a ravel().

almost had it @tacaswell!  Not bad for off the top of your head
DOC: Put todo's in re: masking
MNT: Added caswell's tests for the gridder

Merge remote-tracking branch 'caswell/recip_test'

Conflicts:
	nsls2/recip.py
	nsls2/tests/test_recip.py
MNT: Updated tests to cover more code
MNT: Un-deleted tests
DOC: Verbosified the test function name
Merge pull request #143 from ericdill/gridder_tests

TST : Gridder tests
MNT: Fixes based on @tacaswell's comments.
Merge pull request #139 from ericdill/grid_mask

ENH: Added binary_mask as input parameter for grid3d
Merge branch 'master' into net_cdf