deal with unsynchronization (read)

I came accross some files which had the unsynchronization bit set to 1, and the library didn't take it into account, thus reading completly false data
This patch is for reading such file only. I don't have yet to write tags, but the simplest way to do it is to put the unsynchronization bit to 0 and rewrite all tags.
This patch may need some factorisation, but I'm not sure where to put the unsynchronizationRead function