Issue #23 finally fixed

This is an old assertion failure, reported for the first time last August. I couldn't fix this until now because I couldn't reproduce the crash. Recently somebody else mailed me a file that exhibits the same issue, which allowed me to provide a fix.

Time for two more crash fixes

I got several reports in the mail about crashes. This release addresses two of them:

1) Crash if frames in ID3V2 have invalid size.
2) Crash if the backup directory couldn't be created.

The fixes have been in Subversion for a while, but I was hoping I could fix a few more issues before making a new release. Unfortunately I didn't get to a point where I could understand what was happening on somebody's computer or reproduce the problem on mine, so I guess more crash-fix releases will be needed.

There's another small change in the generic Linux binaries: until now they were put directly in a bz2 archive. I realized that this way the users had to set the executable bit themselves, so now I put them in a .tar first.