Improved command line handling of alternative maximum slab sizes.

The first patch fixes handling of -I arguments. Traditional memcached behaviour and fatcache usage text both dictate the argument should be specified in bytes. Internally it was being treated as if it were megabytes.

The second patch, again for traditional memcached compatibilty (existing scripts, config files,etc), adds the ability to append a unit suffix k/K or m/M to specify the slab size as KiB or MiB, respectively, via the command line.