Use .travis.yml based on Pkg default for new packages

`git fetch --unshallow` looks like it's throwing errors
(https://travis-ci.org/JuliaStats/DataFrames.jl/builds/14701699)
Revert "Use .travis.yml based on Pkg default for new packages"

This reverts commit 09d4b3f8aad81883b467017638960368fbc12997.
Update git before trying to unshallow
Updates to sorting interface to better match mainline julia

* Allow user to specify sort order by keyword/column tuple or array
  (e.g., rev=(true,false,false)
* Allow user to specify sort order by order(...) function
  (e.g., order("colname", rev=true) )
* Added issorted(...), and accept the same kw arguments
* Added tests
* Added docs
Merge pull request #389 from kmsquire/sorting_update

DataFrame sorting update