Fix iterating over DateTime by doing strict checking for Time objects

- Fixes #13667
Merge pull request #13668 from prathamesh-sonpatki/issue-13667

Fix iterating over DateTime by doing strict checking for Time objects
fixes the Gemfile generator templates

The templates were written as if for a given gem you could either pass a version
or options, but not both. But you may want to specify a version and also a group
or whether the gem has to be required, for example.
upgrade SDoc

Kudos to @zzak for taking over SDoc and make it work with RDoc 4.
fixes a typo in a CHANGELOG
Skip Spring App Generator tests on JRuby

Spring makes extensive use of Process.fork, so won't be able to provide
JRuby Support, hence skip these tests on JRuby.
Merge pull request #13673 from senny/use_enum_label_in_forms

use enum labels as form values. Achieved by `_before_type_cast`.
Merge pull request #13646 from jenseng/json_escape

Clarify behavior of json_escape [ci skip]
Merge pull request #13687 from gaurish/spring-has-no-love-for-jruby

Skip Spring App Generator tests on JRuby
doc proc/lambda arg on inclusion validation. Closes #13689. [ci skip]
highlight http://localhost:3000 in README.md. Closes #13643. [ci skip]

This has no effect on the API docs. The main API page is taken from:
    railties/RDOC_MAIN.rdoc
fix bug in becomes! when changing from base to subclass. Closes #13272.
standardize on jruby_skip & rbx_skip

This Adds helpers(jruby_skip & rbx_skip). In Future, Plan is to use
these helpers instead of calls directly to
RUBY_ENGINE/RbConfig/JRUBY_VERSION
Merge pull request #13693 from gaurish/typo

[JRuby] Fix incorrect RUBY_ENGINE value
setup Bundler in engines `bin/rails` stub.

This is necessary when bundling gems locally using `BUNDLE_PATH`.
Without this patch `bin/rails` fails with:

```
/Users/senny/.rbenv/versions/2.0.0-p353/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- rails/all (LoadError)
	from /Users/senny/.rbenv/versions/2.0.0-p353/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from bin/rails:7:in `<main>'
```
Updated Changelog to reflect removal of :dependent => :restrict

Based on https://github.com/rails/rails/issues/2502, the option has
been removed.
Merge pull request #13699 from rystraum/dependent-restrict-removal

Updated Changelog to reflect removal of :dependent => :restrict
Only lookup `config.log_level` for stdlib `::Logger`. Closes #11665.

This prevents Rails from assigning meaningless log levels to third
party loggers like log4r. If `Rails.logger` is not `kind_of?(::Logger)`
we simply assign the `config.log_level` as is.

This bug was introduced by #11665.
removed extra comma [ci skip]
Merge pull request #13702 from kuldeepaggarwal/docs-fix

removed extra comma [ci skip]