add 'restart' character to ast_control_playback function and ControlPlayback()...

add 'restart' character to ast_control_playback function and ControlPlayback() application (issue #4693)
rework app_controlplayback.c to take into account all Asterisk 1.2 coding style requirements


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@6352 65c4cc65-6c06-0410-ace0-fbb531ad65f3