Support "query_flags" parameter for Groonga's "select" command (partially)

Currently, only these flags are avaiable: ALLOW_PRAGMA, ALLOW_COLUMN, and NONE.

And, allowPragma becomes true by default by the spec of Groonga's select command.
See: http://groonga.org/ja/docs/reference/commands/select.html#query-flags
Update expected conditions for fixed spec of Groonga's select command