Revert "Merge pull request #11 from genki/master"

This reverts commit 83a1a8eb3e19bd2e9b6218443d3de1270f5e5fe2, reversing
changes made to fd195aa5e614123636c3cc3268e07049a2fe8463.

This problem is fixed in groonga at
69b1a0e92ed0249165cdb6b209181c6cea961fdc.