New exec_record_done variables

New variables are added to exec_record_done directive to make setting files and directories easier.

• filename - file name portion of the path, directory omitted
• dirname - directory path
• basename - file name with file extension omitted

Assume path is /tmp/rec/mystream-1389499351.flv. Then filename is mystream-1389499351.flv, dirname is /tmp/rec, basename is mystream-1389499351.

Example of recording mp4 with proper file names.

application myapp {
  live on;
  record all;
  record_path /tmp/rec;
  record_unique on;
  record_interval 30s;
  exec_record_done ffmpeg -i $path -c copy /var/videos/$basename.mp4;
}

Wiki is updated as well.