--sizeonly option (skip checksum for localfiles)

[twi11ie]

I have a folder with thousands of files and I didn't want the HD to crank out checksums every time I added a new files and did a sync.  So I updated the s3sync to have a --sizeonly flag where it only compares the sizes (and not the checksums).  Is this something everyone else would be interested in?  It only took 2 minutes to add but I could upload the diff.

[ferrix]

Please do.  This is something I've thought about doing myself but haven't yet; mostly because I wanted to try and do some kind of timestamp check to make up for it (which is non-trivial to accomplish)