Specific exception for when an extended template doesn't exist

[Unai Zalakain]

#8116 defines a specific exception for when included templates doesn't exist (IncludedTemplateDoesNotExist). The reason for that is that otherwise, the normal TemplateDoesNotExist is swallowed by django.template.loader.select_template.

While there's no any problem with TemplateDoesNotExist being raised when an extended template doesn't exist, it could maybe be beneficial to raise a more specific exception, I don't know.

[chrismedrela]

django.template.loader.select_template doesn't swallow TemplateDoesNotExist since ​​https://github.com/django/django/commit/e2f06226ea4a38377cdb69f2f5768e4e00c2d88e so there is no need for IncludedTemplateDoesNotExist, so we don't have any reason to change the class hierarchy of template exceptions. If I'm missing something, feel free to reopen this ticket.