Duplicates in the mounted dir are still possible

[slowpeek]

There was issue #59 when icons in apache listing produced duplicated items in the mounted dir. It was resolved by checking, if two consequent urls are the same in e76b079

But there could be other occasions for the same file being mentioned more than once in http listings. For example, in https://cdimage.ubuntu.com/daily-live/current/, you can see there is a header above the actual listing, which offers two quick links for two iso images. Having it mounted, I see this:

$ ls -l
total 17857924
-r--r--r-- 1 chun chun 5640202240 Dec 14 08:20 plucky-desktop-amd64.iso
-r--r--r-- 1 chun chun 5640202240 Dec 14 08:20 plucky-desktop-amd64.iso
-r--r--r-- 1 chun chun   12393248 Dec 14 08:23 plucky-desktop-amd64.iso.zsync
-r--r--r-- 1 chun chun      18539 Dec 14 08:20 plucky-desktop-amd64.list
-r--r--r-- 1 chun chun      57748 Dec 14 08:13 plucky-desktop-amd64.manifest
-r--r--r-- 1 chun chun 3493376000 Dec 14 08:22 plucky-desktop-arm64.iso
-r--r--r-- 1 chun chun 3493376000 Dec 14 08:22 plucky-desktop-arm64.iso
-r--r--r-- 1 chun chun    6823221 Dec 14 08:24 plucky-desktop-arm64.iso.zsync
-r--r--r-- 1 chun chun       9685 Dec 14 08:22 plucky-desktop-arm64.list
-r--r--r-- 1 chun chun      56810 Dec 14 07:58 plucky-desktop-arm64.manifest
-r--r--r-- 1 chun chun        182 Dec 14 08:25 SHA256SUMS
-r--r--r-- 1 chun chun        833 Dec 14 08:25 SHA256SUMS.gpg

Both iso images are listed twice.