Case-sensitivity in filelists

[maksis]

Starting from version 3.30, AirDC++ refuses to load filelists that contain directories with duplicate names in case-insensitive context (since such lists are malformed according to ADC/NMDC specs). However, this has caused some problems, since at least Eiskalt and Flylink will happily generate filelists with duplicate item names.

I noticed that DC++ seems reject filelists that contain duplicate item names but only if the casing is equal (https://sourceforge.net/p/dcplusplus/code/ci/0d3e46e86e5e21d6382fa72d6f75944dac40d62f/tree/dcpp/DirectoryListing.h#l77), which is probably also related to https://bugs.launchpad.net/dcplusplus/+bug/1619916
However, item lookups made by path are case-insensitive (https://sourceforge.net/p/dcplusplus/code/ci/0d3e46e86e5e21d6382fa72d6f75944dac40d62f/tree/dcpp/DirectoryListing.h#l165). Depending on how the core is being used, that might raise some security concerns as lookups made by path may return different items that were requested (since the items are not unique in case-insensitive context).

What was the motivation behind making the filelist directory/file sets case-sensitive? I don't know if I did everything correctly, but based on my testing, the current case-sensitive comparison function is also terribly slow: changing it to case-insensitive Util::stricmp reduced the loading time of my test filelist from 70 seconds to 42 seconds.