Print progress during dd.
Print progress during dd.

Useful to estimate how long a dd will take.

The progress flag may be one of the following:

    none: nothing extra is printed to stderr
    xfer: print transfer stats after completion (default)
    progress: progressively print transfer stats during copy (GNU)

I performed a bit of benchmarking and the addition of the feature has no
noticeable penalty on performance.

Signed-off-by: Ryan O'Leary <ea3cd978650417470535f3a4725b6b5042a6ab59@ryanoleary.ca>

u-root/u-root,hugelgupf/u-root,rminnich/u-root,hugelgupf/u-root,u-root/u-root,rminnich/u-root,GanShun/u-root,GanShun/u-root,u-root/u-root,hugelgupf/u-root,rminnich/u-root,GanShun/u-root,hugelgupf/u-root,rminnich/u-root