Some time ago, when there was no support of boolean type in SQL, boolean
values passed as parameters to be bound were converted to integer values
0 and 1. It takes place in lua_sql_bind_decode(). However, now we can
avoid this conversion and store booleans as booleans. Note that patch
does not include test case since type of value is preserved correctly,
so when binding is extracted from struct sql_bind it will assigned to
the right value.