[suggestion] support non-negative float number in git-repack --max-pack-size

Hi,

I would like to create packfiles with charm-numbered size (that is for 
example use 49.99M instead of 50M) with git-repack:

$ git repack --max-pack-size=49.99M -a -d

But Git didn't support it:

error: option `max-pack-size' expects a non-negative integer value with an optional k/m/g suffix

The workaround was scaling down to kibibytes:

$ git repack --max-pack-size=52418K -a -d

But the workaround is a rather convoluted to me, because I must convert 
mebibytes (MiB) to kibibytes (KiB). I had to multiply the desired 
packfile size by 1024, as opposed to by 1000 in familiar size notation 
(kilobytes [KB] and megabytes [MB]).

It would be nice if non-negative floating-point number can be allowed in 
--max-pack-size option, so that many users don't have to scale down size 
notation like above.

PS: charm numbers are most often used in pricing, because it's almost 
used everywhere (part of psychological pricing).

Thanks.

-- 
An old man doll... just what I always wanted! - Clara