* tta/perl/Texinfo/Indices.pm (element_index_content_element),
tta/C/main/manipulate_indices.c (element_index_content_element):
rename document_index_content_element as
element_index_content_element. Update callers.

* tta/C/main/manipulate_indices.c (index_entry_element_sort_string)
(setup_index_entries_sort_strings): add an explicit document argument.
Update callers.

* tta/C/main/manipulate_indices.c (index_entry_element_sort_string),
tta/perl/XSTexinfo/parser_document/IndicesXS.xs
(index_entry_element_sort_string): set debug_level to valid values,
based on options in setup_index_entries_sort_strings and
directly use debug_level in argument in
index_entry_element_sort_string.