download_strategy: fossil now outputs hash:

[EricFromCanada]

URLs using :fossil checkouts haven't worked since fossil switched from printing uuid: to hash: for fossil info tip.

Also, fix this error for CVS checkouts:

$ brew fetch -s -v --HEAD mandoc
==> Cloning anoncvs@mandoc.bsd.lv:/cvs
/usr/bin/env PATH=/usr/bin:/opt/homebrew/opt/cvs/bin:/opt/homebrew/Library/Homebrew/shims/shared:/bin:/usr/sbin:/sbin cvs -d anoncvs@mandoc.bsd.lv:/cvs checkout -d /Users/eric/mandoc--cvs mandoc
Warning: Permanently added 'mandoc.bsd.lv' (ED25519) to the list of known hosts.
cvs [server aborted]: absolute pathname `/Users/eric/mandoc--cvs' illegal for server
Error: Failed to download resource "mandoc"
Failure while executing; `/usr/bin/env PATH=/usr/bin:/opt/homebrew/opt/cvs/bin:/opt/homebrew/Library/Homebrew/shims/shared:/bin:/usr/sbin:/sbin cvs -d anoncvs@mandoc.bsd.lv:/cvs checkout -d /Users/eric/mandoc--cvs mandoc` exited with 1. Here's the output:
Warning: Permanently added 'mandoc.bsd.lv' (ED25519) to the list of known hosts.
cvs [server aborted]: absolute pathname `/Users/eric/mandoc--cvs' illegal for server

[Bo98]

Do we need/want backwards compatibility with older versions?

[EricFromCanada]

I doubt it; the current version's prebuilt binary (2.26) runs on 10.13+ and compiles from source on earlier versions, so I don't see any reason for 2.11 and earlier to still be out in the wild. But it's an easy fix so I added it anyway.

[MikeMcQuaid]

Thanks @EricFromCanada!