Address edge case for number_to_human with units option.

ActiveSupport::NumberHelper#number_to_human now returns the number unaltered when
the units hash does not contain the needed key, e.g. when the number provided is less
than the largest key provided.
Fix backwards compatibility with Rails 3 apps.

When we removed script/rails and introduced bin/rails, we accidentally
introduced a regression. If you install Rails 4 as a gem, then try to do
something in a Rails 3 application:

    $ rails g

This will throw the 'please type rails new foo' message rather than the
proper generator documentation message. This is because older apps don't
have bin/rails.

Therefore, we now *prefer* bin/rails, but still search for script/rails,
and exec the one we find.
Correct comment for (beginning|end)_of_minute
Merge pull request #9384 from eval/documentation_of_minute

Correct comment for (beginning|end)_of_minute [ci skip]
Merge pull request #9347 from hoffm/number_to_human_bug

Address edge case for number_to_human with units option.