TEST scale_mri:  use smaller source space and python setup_source_space()
DOC add_source_space_distances() error message
TEST scale_source_space() with distances (BK)
FIX scale_source_space():  add distances with 3 scaling params
OPT TEST:  test_scale_mri()
OPT TEST test_scale_mri():  delete all but one label file
DOC:  whats-new
Merge pull request #1478 from christianbrodbeck/fix-scale-ss

Fix scale_source_space