run-tests: drop fallback for sysconfig for pre-py2.7

largefiles: move identical statement to after if/else

util: rewrite sortdict using Python 2.7's OrderedDict Pattern copied from https://docs.python.org/dev/library/collections.html#ordereddict-examples-and-recipes.

encoding: use i.startswith() instead of i[0] to eliminate py2/3 divergence

test-casefolding: sync with latest code changes This goes with c2380b448265.

perf: always pass node to revlog.revision() I removed this in 73c3e226d2fc thinking it wasn't necessary. In fact, we need to always pass a node so the code is compatible with revisions before d7d64b89a65c. The new code uses a variable to avoid check-style complaining about "r.revision(r.node(" patterns.

hg: backout optimizing for treemanifests It turns out that the files list is not sufficient to identify with revlogs have changed. In a merge commit, no files could've changed but directories would have. For now let's just backout this optimization.