Implement our own sqlite3_exec

Should fix issue related to unlock notify: #767
Caveat: many CString allocated.

src/pragma.rs

@@ -256,8 +256,7 @@ impl Connection {
         // The two syntaxes yield identical results.
         sql.push_equal_sign();
         sql.push_value(pragma_value)?;
-        self.execute(&sql, NO_PARAMS)?;
-        Ok(())
+        self.execute_batch(&sql)
     }
 
     /// Set a new value to `pragma_name` and return the updated value.