ENH: locate adds a column for 'frame' using Frame.frame_no
DOC: Add example demonstrating locate with IPython parallel.
BUG: Fix bug in which adding memory particles to a KDTree hash also adds them to the output of link_iter().

Added assert which may catch this if _verify_integrity is turned on.
Fixed placement of comment around memory code in link_iter()
Merge pull request #47 from danielballan/parallel

Parallelizable Locate
BUG: Fix undefined frame_no in batch()
Merge pull request #58 from nkeim/fix-parallel

BUG: Fix undefined frame_no in batch()
Merge pull request #55 from nkeim/fix-copybug

Memory/KDTree bugfix (second try)
ENH: Explicitly check for black image and fail informatively.
Merge pull request #59 from danielballan/black-error

ENH: Explicitly check for black image and fail informatively.