BUG: Bug in multi-index slicing with missing indexers (GH7866)
BUG: fix multi-column sort that includes Categoricals (GH7848)
CLN: refactor _lexsort_indexer to use Categoricals
BUG: Categorical concat should preserve levels (GH7864)
Merge pull request #7850 from jreback/cat_sort

BUG: fix multi-column sort that includes Categoricals / concat (GH7848/GH7864)
PERF: groupby / frame apply optimization
NETWORK: change failing FRED test
Merge pull request #7881 from jreback/apply_optimize

PERF: groupby / frame apply optimization
ENH: Add optional level argument to set_names(), set_levels() and set_labels() (GH7792)
BUG/FIX: gut groupby.filter code, raise on multi-valued filter
Merge pull request #7871 from cpcloud/groupby-filter-fix

BUG/FIX: groupby should raise on multi-valued filter
Merge pull request #7867 from jreback/mi_loc

BUG: Bug in multi-index slicing with missing indexers (GH7866)
TST: fix date parsing issue in test_frame/test_replace_datetime
BUG: Fixed incorrect string length calculation when writing strings to Stata

Strings were incorrectly written using 244 character irrespective of the actual
length of the underlying due to changes in pandas where the underlying NumPy
datatype of strings is always np.object_, and never np.string_. Closes #7858

String types were also not being checked for excessive length, and DataFrames
with strings containing more then 244 characters were producing invalid
dta files.  Attempting to write long strings raises an error now.