#103 Nicer progress bars for flac, etc

[Matthew Strait]

This patch makes the progress bar behavior better when
encoding to formats like flac where the bitrate isn't
known.

Old behavior: Progress bars in both track and overall
displays are always full when encoding. Track display
says "Inf x" and overall says "100%".

New behavior: Track progress bar is half full while
encoding, and the
speed is shown as "? x". Overall progress bar reflects
number of
completed tracks, where a track currently being
encoding counts as 1/2 of a completed track.

The new behavior is triggered by
ginfo->kbits_per_sec==0, so if the user has entered a
dummy bitrate, it will act as before.

My changes don't produce the ideal behavior of actually
showing
second-by-second progress, but it seems that to get
that would require
much more invasive changes.

[Matthew Strait]

Patch that improves progress bar display