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.

test-hardlink: do not test .hg/cache/checklink Linux and BSD have different behavior on "os.link(src, dst)" where "src" is a symlink. That causes test difference. According to POSIX [1]: If path1 names a symbolic link, it is implementation-defined whether link() follows the symbolic link, or creates a new link to the symbolic link itself. So both behaviors are correct. This patch removes the trouble maker "checklink" to make the test pass on both platforms. [1]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/link.html

test-hardlinks: unify two test files into one The "whitelisted" test could be unified using "#if"s.

style: ban [ foo == bar] bashism in tests