Fixed bug in DCS registration
I found that DCS registration is sometimes failed because getting path to result directory is failed.
I used 'readlink' function to get the actual path from the simbolic link, and something error seemed to be happened in this function (maybe the buffer size (100) was too small).
Therefore I changed some parts following:
- replaced that function to 'realpath'
- changed buffer size to 4096,
- made it to terminate with the error message if error is happened.
Also I changed the documentation a bit.