API: <% loop %> and <% with %> only ever create one new scope level (fixes #4015)

[kinglozzer]

Removes up an age-old quirk where every . in <% loop $Foo.Bar.Baz %> would require an extra $Up to “escape” from. That was actually a feature, but I’m yet to see compelling use-case for it and it keeps causing confusion (see #4015).

Yes this will probably cause breakages for people upgrading, but they’re going to be easy ones to fix. I’ve changed the user_error() to an exception, because that way it’s at least possible to see the name of the template that’s affected (even if only the “compiled” line number is shown).

3.x and 4.x:

{$Title}		<!-- Current page title -->
<% loop $Children.Limit(5) %>
    {$Title		<!-- Child page title -->
    {$Up.Title}		<!-- Nothing - equivalent to `$Children.Title` -->
    {$Up.Up.Title}	<!-- Current page title -->
<% end_loop %>

After this change:

{$Title}		<!-- Current page title -->
<% loop $Children.Limit(5) %>
    {$Title		<!-- Child page title -->
    {$Up.Title}		<!-- Current page title -->
    {$Up.Up.Title}	<!-- Exception: Up called when we're already at the top of the scope -->
<% end_loop %>

[tractorcow]

I need to merge up fixes for master behat.

[tractorcow]

I've merged up a couple fixes for both testsession + behat-extension. Let's see if that gets the tests running properly.

[kinglozzer]

I should probably remove that E_USER_ERROR...

[tractorcow]

I've merged up all the branches for core modules to master. Let's see if this gets the tests green.

[tractorcow]

Tests are green and the code looks ok, but I really need to do some testing and research to check there are no regressions.

[tractorcow]

FYI I used this template to test and it appeared to produce much more expected output.

<% include SideBar %>
<div class="content-container unit size3of4 lastUnit">
	<article>
		<h1>$Title</h1>
		<div class="content">$Content</div>
        <% if $Parent %>
            <h2>all siblings</h2>
            <% loop Parent.Children %>
                <div>Menu: $Title, Up title: $Up.Title</div>

                <h3>Nested</h3>
                <% loop Parent.Children %>
                    <div>Menu: $Title, Up title: $Up.Title, Up up title: $Up.Up.Title</div>
                <% end_loop %>
                <h3>end nested</h3>
            <% end_loop %>
            <h2>first sibling</h2>
            <% loop Parent.Children.Limit(1) %>
                <div>Menu: $Title, Up title: $Up.Title</div>
            <% end_loop %>
        <% end_if %>
	</article>
</div>

[tractorcow]

The logic goes over my head a little, but the effect seems to have resolved the usability issue. I'm inclined to merge this and hope that the future will be kind. ;)