ActionView::Helpers.asset_path is where the logic for
javascript_include_tag resides.  It takes an extname option for
specifying the extension or false to not append it.  This exposes that
option to javascript_include_tag.

Without the option files that didn't end with ".js" would get the
extension appended to them.  This broke JST templates and other file
types that should be interpreted as JavaScript but who's file extension
isn't ".js"

Fixes warning

warning: URI.unescape is obsolete

In some cases webservers like nginx send the escaped characters
lowercased to the Rails application. The current_page? helper was
comparing the escaped strings that are different since Ruby escapes the
URL using uppercased characters.

This fixes potential thread safety issues introduced in 09f6fe1c. The problem
with the original code was that the "recursion-stopping" `nil` values could
be seen by other threads.

content tag already knows which tags are boolean and the values that
should generate them when a truthy value is passed, so leave this logic
for it instead of duplicating when generating options tags.

Fix default rendered format problem when calling render method without :content_type option. Closes #11393.

When rendering recursive partial Action View is trying to generate the
view digest infinitly causing a stack level error.

Fixes #11340

Control to output a hidden input tag with name `utf8` without monkey
patching

Before:

    form_tag
    # => '<form>..<input name="utf8" type="hidden" value="&#x2713;" />..</form>'

After:

    form_tag
    # => '<form>..<input name="utf8" type="hidden" value="&#x2713;" />..</form>'

    form_tag({}, { :enforce_utf8 => false })
    # => '<form>....</form>'

Use link_to with block and url_hash, expect block as name.
But ignore block and use url_hash as name.
3-2-stable passes this test. 4-0-stable and master fail this.

Pass in an :include_seconds hash option to use this feature.

Move the write portion of fragment_for to its own method to allow for easier creation of custom cache methods.

This commit creates structure for Action View gem and is first of a
series of commits extracting Action View from Action Pack.