datetime review part 2 [Update 7]

[Jonathan M Davis]

Most recent code: http://is.gd/hYwOV

I fixed the Mac-specific code with what Michel gave me. So, hopefully that works 
now. tzset has been added do druntime for the Mac in svn, so hopefully with that 
fix, datetime.d will compile and run properly with the tests passing on Mac OS X. 
However, I obviously haven't tested it, since I don't have a Mac.

Other than that, just a few documentation fixes. So, if you're not on a Mac, the 
this update shouldn't change anything for you.

- Jonathan M Davis


P.S. Remember to link with advapi32.lib on Windows.