HarlanH/DataFrames.jl — pull request #194 by simonbyrne (2013-02-14 09:10:17+00:00)
Title: Add period to list of missingness indicators

A period is often used as a missingness indicator (e.g. SAS), also mentioned in Wilkinson's statistics quiz:
http://www.stanford.edu/~clint/bench/wilk.txt