fix #34 

The old code intends to normalize every column to lower or upper case. 
This makes it difficult if we create a table with two columns that are almost the same:

create stream v(id int, Id float)

also because writing to csv the header is lowercase, we need to convert it to keep the old name.


the side effect: 
when importing a csv from other systems instead sling prob has an issue.
and I was thinking of the current PR hard code in many places,  need some time to prepare before sending it upstream.