TST: Use tempfiles in all tests.

Includes @jreback's commits from #5422 and hdf_temp:
* TST: make pytables tests go thru a temporary dir and file
* TST/BUG: incorrect way of testing for r+ modes

TST: fix temporary files by using mktemp (rather than mkstemp) which opens them
BUG: not clearing the cache when reindexing issue when partial setting (GH5424)
TST: provide temporary file creation inside of io/pytables.py directly w/o
     opening a named temporary file
TST: named temporary file creation back to mkstemp in utils/testing.py/ensure_clean
Merge pull request #5426 from jreback/indexing_cache

BUG: not clearing the cache when reindexing issue when partial setting (GH5424)
Merge pull request #5425 from jreback/temp_file

TST: Use tempfiles in all tests.
BUG: to_timedelta of a scalar returns a scalar, closes #5410.
Merge pull request #5415 from danielballan/to-timedelta-scalar

BUG: to_timedelta of a scalar returns a scalar, closes #5410.
BUG/TST: bug in the test apparatus when dtypes are equal in a Series but the
         values are not equal
Merge pull request #5434 from jreback/test_fix

BUG/TST: bug in the test apparatus when dtypes are equal in a Series but the values are not equal
Fix Issues with FY5253 and variation=nearest w/ year end in Dec
Reordered DateOffset classes after merge
ENH: Add mode method to Series and DataFrame

Abstract building up the tables with counts so value_count and mode can
share. Aww! DOC: Add documentation about mode()
CLN: Mode result needs to be sorted, otherwise hit weirdness with hashing
Merge pull request #5380 from jtratner/add-mode-to-series-and-frame

ENH: Add mode method to Series and DataFrame
Added failing test case for resampling TimeSeries by period with a local timezone.

Related to #5340.

Signed-off-by: Kevin Stone <kevinastone@gmail.com>

Added Test Case for #3609.

Signed-off-by: Kevin Stone <kevinastone@gmail.com>

Fixes Grouping by Period with Timezones

The timestamp generated to partition the data frame doesn't include timezone information, so it was creating the wrong groups.  It also had the frequency ('D') hard coded.

Fixes #5340 and #3609.

Signed-off-by: Kevin Stone <kevinastone@gmail.com>
ENH: Always do true division on Python 2.X

Note: this version actually forces `a / b` to always do truediv as well.
It's less complicated to maintain if we do it that way, but it's also
possible to have this `a / b` use div and `a.div(b)` use truediv, just
might be strange. This is definitely different from numpy behavior.

We also may need to add the division future import to more places.
DOC: Add notes about truedivision
Merge pull request #5439 from jtratner/make-div-do-truediv

ENH: Always do true division on Python 2.X
ENH: Better handling of MultiIndex with Excel

Added merged cell formatting for MultiIndex and Hierarchical Rows.
Issue #5254.
API: raise SettingWithCopy when chained assignment is detected