fix time_tag helper and update tests to not rely on dynamically generated values

  Before `time_tag Date.today` will return `<time
  datetime="2013-02-14T00:00:00+00:00">February 14, 2013</time>`.
  This commit fixes time_tag helper to use RFC-3339 full-date format
  (Y-m-d) in datetime attribute.
document setting custom datetime attribute for time_tag helper
Merge pull request #9334 from NARKOZ/time_tag

use ISO 8601 format in time_tag helper
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.
Changelog improvements, use 1.9 style hash in examples [ci skip]
Move number_to_human test from AP to AS

Since all changes from #9347 are related to AS, it seems proper that the
test is placed there as well.
Fix debug helper not inspecting on Exception

The debug helper should inspect the object when it can't be converted to YAML, this behavior was changed in 8f8d8eb1465069e2ed9b6f2404aa9d02e785f534.
Merge pull request #9387 from boukevanderbijl/master

Fix debug helper not inspecting when it can't convert to YAML
forwardport #9388 rename/remove column preserves custom PK.
rename_column_test.rb -> columns_test.rb to reveal intent.

I renamed the test to better communicate it's intention. Since it also tests:
  - add_column
  - remove_column
  - change_column
There is no reason to call it rename_column_test.
Merge pull request #9389 from senny/forwardport_9388

Forwardport #9388 rename/remove column preserves custom PK.