Fix bug : Some content file doens't downloaded.

In case of some content file, FileIO error is raised at the moment of last
stage of download - rename to real file name from temp file.
Ext4 uses 255 bytes for file name, and max. file ame length was set as 127
(255/2 because java uses 2 bytes as 'char' type)
But, Linux uses UTF-8 encoded file name. So, 255/2 is wrong calculation.
This issue is fixed by changing max. file name length into 255/4 = 63
(UTF-8 uses 1-4 bytes)