BUG: fix CategoricalBlock unpickling

TST: add categorical frame and series to generate_legacy_pickles

TST: generate legacy pickle including frames/series with categoricals
for 0.15.0

COMPAT: ensure pre-0.15.0 pickles of Categorical are read

TST: move assert_categorical_equal to tm.TestCase
API: Raise more specific exception on concat([None])
Merge pull request #8519 from immerrr/fix-categoricalblock-pickling

BUG: fix CategoricalBlock pickling
Add xray to ecosystem docs

Fixes #8516
Merge pull request #8534 from shoyer/add-xray-to-ecosystem-docs

Add xray to ecosystem docs
DOC: Add 29+ in-line examples, change headings & intro to cookbook GH6918
Merge pull request #8288 from jnmclarty/cookbook_inline_examples

Cookbook Inline Examples 2014Q3
BUG: Dont add None to plot legend.
Merge pull request #8536 from TomAugspurger/plot-label-none

BUG: Dont add None to plot legend.
PERF: Performance improvement for MultiIndexes with a DatetimeIndex level
DOC: Clean Cookbook Issues: Tabs, expanded_apply, axis aliasing, etc.
Merge pull request #8535 from jnmclarty/cookbook_inline_examples

DOC: Clean up Sphinx Issues, fix tabs, in Cookbook
Merge pull request #8544 from mtkni/master

PERF: Performance improvement for MultiIndexes with a DatetimeIndex levels
DOC: v0.15.0 corrections
DOC: Update ecosystem.rst: Add IDE, IPython, qgrid, Spyder, API, quandl, Out-of-core, Blaze

DOC: Update ecosystem.rst: Add IDE, IPython, API
DOC: Update ecosystem.rst: Add GUI > Spyder
DOC: Update ecosystem.rst: GUI -> IDE, IPython > qgrid, API
DOC: Update ecosystem.rst: -> IDEs
DOC: Update ecosystem.rst: depluralize
DOC: Update ecosystem.rst: Add IPython [Notebook] description; alphabetize
DOC: Update ecosystem.rst: add Blaze, alphabetize
Merge pull request #8507 from westurner/patch-3

DOC: Update ecosystem.rst: Add IDE, IPython, qgrid, Spyder, API, quandl, Out-of-core, Blaze
PERF: Slowness in multi-level indexes with datetime levels

Special case handling of sliced multi indexes, where there the length of the level values may exceed the length of the index.
Corrected nan handling issue introduced by the original change. (+1 squashed commit)
Squashed commits:
[0dae170] PERF: Slowness in multi-level indexes with datetime levels

Special case handling of sliced multi indexes, where there the length of the level values may exceed the length of the index.
PERF: fixup datetime_index repr perf (GH8556)
Merge pull request #8557 from jreback/dt_perf

PERF: fixup datetime_index repr perf (GH8556)
DOC: formatting issue in scatter_matrix section