The origins of orig_tpl_* are not pretty. Please see the following commits
and associated tickets: r9823, r9839, r9847, r10150, r10460.
In short, multiple hacks were required due to template engine reading
inheritance/storedb flags from $user (global) even when the template that
was being looked up or rendered was not the "active style of the
current user".
We no longer store templates in the database, removing half of the problem.
This commit fixes the second half of the problem by deleting
set_template_path function from template locator, and moving that logic
back into the template class' set_template. set_template now calls
set_custom_template, the latter only taking the template path and the
fallback paths as parameters. With this change template locator no longer
uses $user and does not use phpbb root path either.
All logic involving setting the user's "active" template is now
encapsulated in a single template class's function, set_template.
Setting other templates is done via set_custom_template and the caller
is responsible for determining and passing in fallback/inheritance path,
if any.
PHPBB3-9726
52f208900f