tests/test-casecollision.t

run-tests: fix `HGTESTEXTRAEXTENSIONS` with py3

Since `extensions` was a str and `section` bytes, it never populated anything.
If it had, it would have put bytes into the environment dictionary that is all
str.  As everything starts and ends as str, remove the incomplete attempt at
byteification.  It doesn't appear that we had any test coverage of this bit of
code, so also add a non-extension config to make sure it is filtered out
properly.

Differential Revision: https://phab.mercurial-scm.org/D9557

#require no-icasefs

test file addition with colliding case

  $ hg init repo1
  $ cd repo1
  $ echo a > a
  $ echo A > A
  $ hg add a
  $ hg st
  A a
  ? A
  $ hg add --config ui.portablefilenames=abort A
  abort: possible case-folding collision for A
  [255]
  $ hg st
  A a
  ? A
  $ hg add A
  warning: possible case-folding collision for A
  $ hg st
  A A
  A a
  $ hg forget A
  $ hg st
  A a
  ? A
  $ hg add --config ui.portablefilenames=no A
  $ hg st
  A A
  A a
  $ mkdir b
  $ touch b/c b/D
  $ hg add b
  adding b/D
  adding b/c
  $ touch b/d b/C
  $ hg add b/C
  warning: possible case-folding collision for b/C
  $ hg add b/d
  warning: possible case-folding collision for b/d
  $ touch b/a1 b/a2
  $ hg add b
  adding b/a1
  adding b/a2
  $ touch b/A2 b/a1.1
  $ hg add b/a1.1 b/A2
  warning: possible case-folding collision for b/A2
  $ touch b/f b/F
  $ hg add b/f b/F
  warning: possible case-folding collision for b/f
  $ touch g G
  $ hg add g G
  warning: possible case-folding collision for g
  $ mkdir h H
  $ touch h/x H/x
  $ hg add h/x H/x
  warning: possible case-folding collision for h/x
  $ touch h/s H/s
  $ hg add h/s
  $ hg add H/s
  warning: possible case-folding collision for H/s

case changing rename must not warn or abort

  $ echo c > c
  $ hg ci -qAmx
  $ hg mv c C
  $ cd ..