* FileAccess.cc, commands.cc, history.cc: don't add a slash if it's already there.
* xmap.cc: slightly better hash.
* xarray.h: (xarray_p::qsort) new method.
* StringSet.h: (StringSet::qsort) new method.
* ResMgr.cc, ResMgr.h, Http.cc, resource.cc: use xlist and xmap to manage settings (for better performance).
* Torrent.cc, Torrent.h: save metadata and load if needed; (torrent:save-metadata) new setting.