TST: better assertion messages on test failures

CLN: pep8
Merge pull request #4430 from jreback/testing

TST: better assertion messages on test failures (GH4397)
API: GH4409 HDFStore addes an is_open property to indicate if the underlying file handle is_open;
    a closed store will now report 'CLOSED' when viewing the store (rather than raising an error)

API: HDFStore, removed the _quiet attribute, replace by a ``DuplicateWarning`` if retrieving
     duplicate rows from a table (GH4367)

TST: change warnings filter to assert_produces_warning in test_pytables.py

API: removed the warn argument from open. Instead a PossibleDataLoss exception will
     be raised if you try use mode='w' with an OPEN file handle (GH4367)

API: semantics of close in HDFStore now will close that instance of HDFStore
     the final file close is ref counted (by PyTables) w.r.t all of the open handles

ENH: raise ClosedFileError if an operation is attempted on a closed file
DOC: 10min import fixes
Merge pull request #4417 from jreback/hdf_close

API: GH4409 HDFStore adds an is_open property / CLOSED message
DOC: Fix typo

Fixes minor typo in groupby documentation
Merge pull request #4436 from kyleam/groupby-doc-typo

DOC: Fix typo
TST: test updates for testing
Merge pull request #4445 from jreback/hdf_fix

TST: test updates for testing
DOC: change lzip,lrange in 10min.rst to list(zip(..)) and list(range(..))
DOC: minor 10min.rst import fixes
DOC: lrange, lzip --> list(range and list(zip
TST: util/testing improvements

assertRaises and assertRaisesRegexp are now with-statement-compatible,
refactored assert_panel_equal and removed check_index_freq from
assert_series_equal.
Merge pull request #4450 from jtratner/change-range-zip-in-docs

DOC: lrange, lzip --> list(range and list(zip
Merge pull request #4451 from jtratner/better-assert-tests

TST: pandas/util/testing : test improvements and cleanups