HG: Determine which versions of hg we're supporting

Test which versions felog works for:

• clone mercurial
• come up with a list of revs to run felog on (all of them?)
• Advance back tag by tag, running felog against that version of mercurial for all revs in the repo, until it breaks.

Automated test:

• do the same as above for our supported revisions

Check with IT what version they can support.