It's needed to support `DateTime.parse` on Ruby 1.9.2
```
> rbenv shell 1.9.3-p392
> ruby -rtime -v -e "puts DateTime.parse('2014-01-01')"
ruby 1.9.3p392 (2013-02-22 revision 39386) [x86_64-darwin12.3.0]
2014-01-01T00:00:00+00:00
> rbenv shell 1.9.2-p290
> ruby -rtime -v -e "puts DateTime.parse('2014-01-01')"
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin12.0.0]
-e:1:in `<main>': undefined method `parse' for DateTime:Class (NoMethodError)
> ruby -rdate -v -e "puts DateTime.parse('2014-01-01')"
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin12.0.0]
2014-01-01T00:00:00+00:00
```

Looks like the reason is because later Rubies `require 'date'` automatically when you `require 'time'`:
```
> rbenv shell 1.9.2-p290
> ruby -v -e 'require "time"; puts require "date"'
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin12.0.0]
true
> rbenv shell 1.9.3-p392
> ruby -v -e 'require "time"; puts require "date"'
ruby 1.9.3p392 (2013-02-22 revision 39386) [x86_64-darwin12.3.0]
false
```