fst-bin: don't skip headers

We don't skip headers for 'fst set' or 'fst map --sorted'.
Interestingly, we did skip them for a just plain 'fst map'. The end
affect is that FSTs built with 'fst map' would be missing the first row
from the source CSV file.

Fixes #69

fst-bin/src/util.rs

@@ -160,7 +160,9 @@ impl Iterator for ConcatCsv {
                             Err(err) => return Some(Err(From::from(err))),
                             Ok(rdr) => rdr,
                         };
-                        let csvrdr = csv::Reader::from_reader(rdr);
+                        let csvrdr = csv::ReaderBuilder::new()
+                            .has_headers(false)
+                            .from_reader(rdr);
                         self.cur = Some(csvrdr.into_deserialize());
                     }
                 }