more changes to address travis build failures
Use different order of replicate/arithmetic to make keeping properties easier
More explicit setting of jd1,jd2 in _get_delta_ut1_utc
Fix bug in get_delta_tdb_tt using meters where km expected
Update CHANGES.rst
Update documentation example
Ensure arithmetic keeps track of isscalar properly (plus tests)
Add bug-fix entry to CHANGES.rst
Merge pull request #1929 from taldcroft/time-tdb-tt

Bug in TDB to TT calculation
Merge pull request #1927 from mhvk/time-keep-lon-lat-in-arithmetic

Ensure all relevant Time attributes are passed on in Time addition/subtraction
Add support for OGIP format units.
Merge pull request #1870 from mdboom/unit/recommend

Recommend alternatives when a unit isn't found
Add warning that `Wcsprm` should not be used to get the original values
of keywords in the header.
Call `set` from within the WCS constructor.
Update MaskedColumn to fix unicode column names like in Column
Fix u'' syntax, not in python 3.1, 3.2
Merge pull request #1934 from taldcroft/table/fix-masked-col-name

Update MaskedColumn to fix unicode column names like in Column
Import units on top so u.day, etc., can be used throughout
Squashed commits for masked column pattern change

  Make our MaskedColumn like the example in numpy.ma.tests.test_ma.MSubArray
  Updated implementation; Passes all but 2 tests
  Move most Column stuff into BaseColumn
  Add option to allow converting MaskedColumn to Column in BaseColumn
  Copy mask and change so mask len must match array len
  Add Column.__new__ which mostly calls BaseColumn.__new__, and some cleanup
  Strip off the BaseColumn-ness for repr and str to fix MaskedColumn repr
  Rewrite copy so it works for both Column and MaskedColumn
  Need to adjust fill_value in MaskedColumn.copy
  Remove unnecessary BaseColumn.__str__, MaskedColumn.__array_finalize__
  Further unify copy by making BaseColumn version fully general; improve docstring
  Set fill_value via setter, not MaskedArray constructor
  Residual cleanup from rebase
  Make MaskedColumn inherit from Column to get output methods
  Use six.callable for compatibility with Python 3.1
  Remove a misplaced str() conversion
  Update CHANGES.rst
Replace other use of "u" as variable with "rxy" in TDB calculation