ENH: Add `isin` method to DataFrame.

docs. to be rebased

ENH: Add isin method to DataFrame

Basic tests.

Added method and fixed tests.

ENH: Add ordered argument to df.isin()

Expects a sequence of arrays.

Updated release notes for df.isin()

CLN: cleanup

going to remove ordered argument.

Using a dict for ordered matching. Docs

BUG: fixed subselection length check issues.

Updated release notes for df.isin()

remove merge conflict note
ENH tweak DataFrame isin method
ENH add iloc argument to DataFrame isin
ENH: test_perf.py - use psutil to set affinity (if absent functionality - then affinity module)

original affinity module is not commonly installed, has known issues,
and was not updated since 2006.  psutil is already used in parts of
pandas, so it would be logical to use it instead by default.
minor: some trailing spaces and a pylint "pragma" to stop complaining about Series._ix defined elsewhere
ENH: ujson better handling of very large and very small numbers, throw ValueError for bad double_precision arg #4042
ENH: expose ujson precise_float argument on decode
BUG: explicity change nan -> NaT when assigning to datelike dtypes
Merge pull request #4296 from neurodebian/master

Use psutil to set process affinity (test_perf.py) + minor pylint-friendliness for ._ix
DOC: docs for precise_float option in read_json
Merge branch 'Komnomnomnom-ujson-precise-float'
Merge pull request #4302 from jreback/nat_convert

BUG: explicity change nan -> NaT when assigning to datelike dtypes
Merge pull request #4299 from Komnomnomnom/ujson-small-floats

ENH: ujson better handling of very large and very small numbers, throw ValueError for bad double_precision arg #4042
TST: change a small float comparison to np.allclose
DOC: cookbook addition
Merge pull request #4307 from jreback/ujson_small_fix

TST: change a small float comparison to np.allclose (GH4306)
CLN: remove try suite in _read

A skip will now occur if a call to urlopen or a read from the resulting object
throws a urllib2.URLError exception
DOC: add 0.13 to release notes
TST: make sure test passes even if componnents link isn't present
Merge pull request #4310 from cpcloud/network-failure-hack

TST: make sure test passes even if components link isn't present