NF: Add option to let eventrelated_dataset perform optional temporal compression

or other evil stuff.
RF+BF: Refactor uniquemerge2literal to support multi-dim attributes

This also removes the custom conditional wrapping fo return values into
lists to imply a conversion scheme. Now this function always returns
sequences if it does its job. However, the special case of returning
None for empty sequences and the input for non-sequences are maintained
for backward-compatibility.

Add a dedicated test.
NF: Balancer can re-include "offlimit" samples after balancing

i.e. only balance a portion of a dataset, but keep the rest untouched
and included in the selection.
BF: ensure that t-test returns the proper mean even if compare_to has a value different from zero
Merge remote-tracking branch 'gh-yarik/master'

* gh-yarik/master: (74 commits)
  BF: in case of absent psutil - fix parsingout vmem utilization
  BF: x might be not an ndarray apparently -- fix the check
  ENH: vmem_max debug metric to report peak memory consumption
  ENH: robustify searchlight test
  ENH: in case of an invalid header ensure that the output dataset is centered for world coordinates
  ENH: allow for datasets with invalid nifti header but values for voxel dimensions and element sizes (such as in the hyperalignment example)
  ENH: now comparison in all_equal returns False if the comparison raises an error. XXX is this proper behaviour?
  BF: ensure that the example the tutorial also shows that center_ids are now a feature attribute after running a searchlight
  DOC: minor
  RF+ENH: in the case of a radius of zero only consider the node itself. This speeds things up tremendously in the case of just finding voxels intersecting with the surfaces
  BF: remove silly borrowdoc because it did not apply in the first place
  NF: support for AFNI NIML ROI datasets (.niml.roi when generated in SUMA)
  ENH: minor code cleanup
  NF: support for a null hypothesis mean value in ttest
  ENH: minor code cleanup
  BF: proper variable name c instead of config in augmentconfig. Thanks to Brian Stirling for reporting this
  ENH: in NIML datasets automatically detect the presence of labels and stats. XXX see if we can make this smarter and also detect presence of "targets" label if "labels" label is not present
  BF: ensure that order for elements over rows and columns in numpy arrays is properly written in NIML datasets for binary and base64 output formats
  ENH: another attempt to get test_spatial_searchlight to work properly, this time by changing the boundaries of expected output results rather than @labile tag (which made the test non-responsive according to travis)
  ENH: indicate that test_spatial_searchlight is labile
  ...
ENH: more automagic behaviour to detect sample attribute labels when converting dataset to NIML dset
Added a note into haxby2001.rst on stimuli tarball
PL: minor
NF: pearson correlation on matrices
BF: put the scipy requirement inside the function that calls it
NF: support datasets for correlations
RF: use custom correlation function if p value is not requested
ENH: do not require pad to ico ld value
NF: add a __main__ function so that setup of insta corr can be run from command prompt
RF: overwrite files by default for surfaces
BF: null probablity should be idential under two scenarios
NF: caret binary surface read support
ENH: remove decoding of strings in history
ENH: remove some ugly print statements
ENH: more informative error message if type not understood