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
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