Add confirmation before transfer on unique match.

When dialing by name when there is a unique match the call is transferred to that extension.

Sometimes a caller may misspell a name and match the wrong extension. It would be nice to have an option in the directory settings to direct that a caller be prompted to confirm the correctness of the match before transferring. This would be similar to the behavior when there are multiple matches.

For reference see forum questions http://community.freepbx.org/t/directory-with-confirmation/9000 and http://community.freepbx.org/t/directory-entry-confirmation/27448 .