Categorical: let unique only return used categories
BUG: Resample across multiple days

Fixes an issue where resampling over multiple days causes a ValueError
when a number of days between the normalized first and normalized last
days is not a multiple of the frequency.

Added test TestResample.test_resample_anchored_multiday

Closes #8683
BUG: Fixed font size (set it on both x and y axis). #8765
Merge pull request #8937 from JanSchulz/cat_unique2

Categorical: let unique only return used categories
BLD: run slow tests on new optional build 2.7_SLOW using current versions of everything
BLD: run graphics tests on 2.7_LOCALE using old matplotlib
TST: skip on < mpl 1.3.1 (GH8947)
Merge pull request #8941 from hkleynhans/fix/8683_resample_value_error

BUG: Resample across multiple days
Merge pull request #8949 from jreback/graphics

BLD/TST: skip mpl 1.2.1 tests (GH8947)
TST: Moved test functions to module level. #8023

TST: changed *args, **kwargs to fixed arguments. #8023

TST: Moved rest of the test functions to module level. #8023

TST: patch all module level assert functions to TestCase. #8023

CLN: Cleanup TestCase assert functions pathing #8023
Merge pull request #8940 from papaloizouc/8765_bug_fontsize_only_on_x_axis

BUG: Fixed font size (set it on both x and y axis). #8765
CLN: Add 'is_hashable' predicate to core/common

Some types will pass a test against collections.Hashable but fail when
they are actually hashed with hash().

Introduce a new predicate to help handle these types.

Will use this in subsequent commit.

Test Plan:
In addition to running tests, run the doctest
$ nosetests pandas/core/common.py:is_hashable --with-doc -v
BUG: allow numpy.array as c values to scatterplot

Ensure that we can pass an np.array as 'c' straight through to
matplotlib, this functionality was accidentally removed previously.

Add tests.

Closes #8852