Correct visibility of symbols in (srfi 106).
Correct visibility of symbols in (srfi 106).

Signed-off-by: OGINO Masanori <c49462fef669560e618607913e6c283f7627123c@gmail.com>

omasanori/picrin,koba-e964/picrin,dcurrie/picrin,koba-e964/picrin,picrin-scheme/picrin,leavesbnw/picrin,picrin-scheme/picrin,dcurrie/picrin,ktakashi/picrin,koba-e964/picrin,ktakashi/picrin,leavesbnw/picrin,leavesbnw/picrin,ktakashi/picrin,omasanori/picrin