long click to send file
test MediaPlayer & mediacontroller
done:
1. when long press directory or file, send them to other processer
program according to MIME by a intent.
2. when click a file, if it's mime is start with "audio/", then send it
to mediaplayer with mediacontroller.

problem:
1. mediacontroller view will dispear after 3 seconds. what's the key to
use to call it to show?
2. it seems that hardware key of "back" and "option". "home" key is ok.
maybe related to mediacontroller's interface which main activity
realized.
3. in this 3 seconds that mediacontroller view shows, listview can be
scralled, but tap is no use. maybe this is no problem.