Progress bar update as needed. Fix float() error.

Fixed bug causing the transfer rate code to crash the program when completion reaches
100%.

The updating of the progress bar every loop was killing the CPU performance and
causing the Xorg process to go crazy. By only updating the progress bar if
the percent complete value changes stop this from happening.
Merge branch 'transfer_rate' of https://github.com/tbehan/mintstick into transfer_rate