Add -Dfile to show parsed dag, for debugging, mostly.
fix whitespace
add -Dfile to manpage
Write in dag_file only special and exported variables
fix whitespace
Add support for multiple bindings
spaces for alignment
Treat appending variables as a separate case.

This fixes a bug in which appending to nodes variables would modify dag
variables.
whitespace
Change lookups to multiple bindings
Keep special variables in a set
Change export_list to export_vars set.
Treat resources as just other variables.
Remove category->variables.

They were not useful, and cluttered the code.
Consolidate special vars declarations.
Close over environment for unbinded variables
Move resources from category to nodes
whitespace
Merge pull request #328 from rampantmonkey/makeflow-env-2

Makeflow env 2