Make the OS/platform detection a bit less strange. Simplify the
prettySize function to a more common and logical form.

OS etc:
Remove the BSD4.4 prefix, it's fairly pointless considering.
Avoid using lbs_release outside of gnu/linux.
Fallback to uname in the case that lbs_release is not installed.
Use uname on other Unices regardless.

prettySize:
Should not have any functional change.