spartan: add missing closing tags Browsers apparently don't care about this, but let's fix it for humans.

templatefilters: add commonprefix The commonprefix filter takes a list of files names like files() and returns the longest directory name common to all elements. Differential Revision: https://phab.mercurial-scm.org/D3439

py3: add 3 new passing tests to whitelist We ave crossed the 500 mark! Differential Revision: https://phab.mercurial-scm.org/D3638

serve: add option print-url It can be used to open hgweb in a web browser. Example : xdg-open "`hg serve --print-url`". Differential Revision: https://phab.mercurial-scm.org/D3649

revlog: disallow setting uncompressed length to None Backed out changeset a4942675de6b

unionrepo: fill in uncompressed length of revlog entry It can be either -1 or a valid length, but shouldn't be None. IIUC, we can simply trust the length retrieved from the revlog to be overlaid. I don't bother thinking whether the compressed length can be copied as well. We'll need to fix it later.

fuzz: add clean target Differential Revision: https://phab.mercurial-scm.org/D3677

fuzzutil: make it possible to use absl when C++17 isn't supported Differential Revision: https://phab.mercurial-scm.org/D3676

fuzz: extract some common utilities and use modern C++ idioms Alex Gaynor suggested we should probably copy the left and right sides of diffs to new blocks so we can detect over-reads in the diffing code, and I agree. Once I got into that, I realized we should do things with C++17 idioms rather than keep using malloc() and free(). This change is the result. I tried to split it more than this and failed. Everything still compiles and works in the oss-fuzz container, so I think we can count on C++17 being available! Differential Revision: https://phab.mercurial-scm.org/D3675

tests: update fuzzer tests to include both fuzzers Differential Revision: https://phab.mercurial-scm.org/D3674