Improve csv loading issue 21

Add basic support for header to read_csv
I'll clean up the tests and rebase this once the other PR is merged.
I think it is, or the tests would fail. Since I don't remember the wording of the python closure rules I made a simple script to run locally to see how things get captured and it outputs b as expected:
def panda(a):
    def sup():
        print magic
    magic = "b"
    sup()
panda("a")