Deprecate the Dataset.append() method

We have vstack and hstack for this. They are actually more functional.
It makes little sense to me to have this duplicated. OUr general
paradigm is to yield a new dataset whenever the content is modified,
append() is not following this scheme.
ENH+RF: Introduce a hist() function for datasets

and replace plot_feature_hist() with it.
ENH: Draft of a scikit-learn adaptor
TEST+DOC: Doctest and doc polish for SKLTransformer
Merge remote-tracking branch 'gh-nick/master'

* gh-nick/master: (73 commits)
  ENH: check for hdf5 version in unit test so that only recent versions will check for empty arrays in voxel selection results
  NF: I/O test for empty surface voxel selection results
  BF: fixed merge issue between two branches in unit test
  BF: properly deal with cases when no voxels are near a node yet a fixed radius is used together with outside_node_margin=True. Added unit test to check this specific case
  PL: whitespace fixes
  RF: unit test using array equal
  BF: remove test_gifti as this is part of the surfing unit tests
  BF: unit test uses new "reposition_hemisphere_pairs"
  BF: use new get_sphere_left_right_mapping
  DOC: minor
  RF: better check whether external exists
  ENH: added unit tests
  RF: renamed some methods
  ENH: put a newline at start of searchlight status when in debug mode
  DOC: spacing
  NF: surface generate_bar
  PL: whitespace fixes
  ENH: stack repeated measure results by keeping sample/feature attributes if possible
  RF: fixed a copy-paste error to use proper class name for unit test
  BF: use of _get_single_array returns GiftiArray, not numpy array - set meta data right
  ...

Conflicts:
	mvpa2/tests/test_datameasure.py
Remove trailing whitespace.
Merge remote-tracking branch 'gh-master/master'

* gh-master/master:
  ENH: trying 1-line setup for NeuroDebian repository within travis
  ENH: move trained_{targets,dataset,nsamples} from the Classifier into Learner
NF: Spectral companion for poly_detrend
Merge pull request #134 from hanke/_tent/skl_compat

Another simple wrapper to improve compatibility with sklearn
TEST: Improve hist() testing.
ENH: Let hist() work with plain arrays

In case someone is mistaken our hist with the original one.
ENH: Try to support ancient scipy.filtfilt()
ENH: Convert IIRFilterMapper arguments into parameters
BF: Property access
BF: Not so fast
Merge pull request #133 from hanke/_tent/hist_plot

ENH+RF: Introduce a hist() function for datasets
Merge pull request #135 from hanke/_tent/iir_filter

NF: Spectral companion for poly_detrend
TST: a simple usecase for a mapper which would perform remove_invariant_features
ENH: Use our own warning system for deprecation messages.
Merge branch 'master' of https://github.com/nno/PyMVPA

* 'master' of https://github.com/nno/PyMVPA: (35 commits)
  ENH: include subject id in qa png generation
  ENH: check for external matplotlib & use different ("Agg") renderer that should not be dependent on having an X windows display
  BF: support both skullstripped and non-skullstripped input volumes for QA image plotting
  NF: plot_slices + qa added to prep_afni_surf
  NF+ENH: support for +orig and +tlrc expvol, and ensure resampling to LPI format
  ENH: show error when no surfaces are present
  PL: cleanup
  BF: move fix_cut_surfaces from Make_Spec_FS to MapIcosahedron
  NF: makesurfmask step to generate mask of voxels covered by surface
  NF: support for "-T" option to indiate the expvol is in template space
  BF: flat surfaces merged are optional; throw an info message rather than an error if not present
  NF+BK: support flat surfaces (only full.patch.flat for now) in prep_afni_surf
  NF: use -fix_cut_surfaces when converting FS surfaces
  NF+BK+RF: support for minimal surface-based voxel selection where original node-to-voxel mapping only contains nodes on the high-res surface that are also on the low-res surface. This breaks previous functionality in the unlikely case that someone specified an intermediate surface to VolSurf.__init__ (or its subclasses) that was different from the average of the outer and inner (high-res) surfaces
  ENH: better from_any in volume_mask_dict
  NF: from_any for voxel selection results
  NF: minimal dataset from voxel selection
  ENH: use number of voxels per node with two decimals
  DOC: removed commented-out code
  RF+BK: use "voxel_node_mapping" rather than "use_minimal_mapping" as argument for voxel selection
  ...