Make force_sort_within_sections respect case

force_sort_within_sections only looked at the order_by_type
option to determine how to order imports with different case
in a section. Whether you order import names by type or not
also affected the order of the modules.

When force_sort_within_sections is used:
* ignore case on the module name if case_sensitive is false,
* ignore case on the imported names if order_by_type is false.