Apple renames OS X to macOS. Announced @ WWDC 2016

.com.apple.timemachine.donotpresent is a system file created by TimeMachine on OSX by user choice.

In addition to `.Spotlight-V100` and `.Trashes`, the following dotfiles
may appear at the root of all OSX volumes (not just external disks):

- `.DocumentRevisions-V100`: auto-save and versions storage
- `.fseventsd`: file system event storage
- `.Temporaryitems`: temp directory used by some applications instead of
                     /tmp and /var/tmp
- `.VolumeIcon.icns`: storage of custom icon for volume, if set

The .gitignore rule "Icon?" will also match directories such as
"icons/", at least on a case-insensitive file-system (this happened to
me on OS X 10.7). I only noticed this several days later because a
developer was complaining about missing icons in his repository. I don't
really know what type of files this rule is supposed to match, but I
guess the described behavior is not expected.

In Global/OSX.gitignore .DS_Store? didn't match .DS_Store (a question mark (?) matches a single character).

Ignore files generated by OS X that might appear on external disks:
  .Spotlight-V100
  .Trashes

Ignore files generated by OS X that might appear on external disks:
  .Spotlight-V100
  .Trashes