remove unnecessary code breaking special chars

parsing a spec twice is bad. don't do it for now.

this fix should make column names with spaces work.
e.g. the multi_word example case
Fix type coercion of empty strings to date (return null)

Reviewer: raymond
Fix unreachable code in layers

Reviewer: raymond
Reviewer: lisa
Make local filtering resilient to litter in filter spec

Reviewer: raymond
Remove unnecessary double null/undefined check

Reviewer: lisa
Bug fix for _.isEmpty(<number>) == True
Changes to make joins work.
s/varliable/variable/g
Merge branch 'develop' into ft-derivedvar

Conflicts:
	polychart2.js
	polychart2.min.js
	polychart2.standalone.js
	src/dataprocess.coffee
	src/parser.coffee