Fix gtfs

Fix #298

still need to work on the handling of '\' in csv files (for #297), but since it does not seems possible to handle it with boost tokenizer, it may be quite a serious refactoring (and with impact on all csv).

I don't know yet what is the best course of action:
 * ask to double the slashes in the data
 * change the string before hand to double the slashes (seems quite uggly)
 * change to boost::spirit to parse the file
 * another way :)

Any suggestion ?