tests: test-module-imports.t works on windows (with backslash path sep)

Transform the backslashes to slashes on windows, because they are eaten up by
the shell. (Similar as done in test-check-pyflakes.t.)

This test will not produce a traceback on windows anymore. But the test still
fails because the detected mixed imports differ.

tests/test-module-imports.t

@@ -1,44 +1,44
 This code uses the ast module, which was new in 2.6, so we'll skip
 this test on anything earlier.
   $ python -c 'import sys ; assert sys.version_info >= (2, 6)' || exit 80
 
   $ import_checker="$TESTDIR"/../contrib/import-checker.py
 Run the doctests from the import checker, and make sure
 it's working correctly.
   $ TERM=dumb
   $ export TERM
   $ python -m doctest $import_checker
 
   $ cd "$TESTDIR"/..
   $ if hg identify -q > /dev/null 2>&1; then :
   > else
   >     echo "skipped: not a Mercurial working dir" >&2
   >     exit 80
   > fi
 
 There are a handful of cases here that require renaming a module so it
 doesn't overlap with a stdlib module name. There are also some cycles
 here that we should still endeavor to fix, and some cycles will be
 hidden by deduplication algorithm in the cycle detector, so fixing
 these may expose other cycles.
 
-  $ hg locate 'mercurial/**.py' | xargs python "$import_checker"
+  $ hg locate 'mercurial/**.py' | sed 's-\\-/-g' | xargs python "$import_checker"
   mercurial/dispatch.py mixed imports
      stdlib:    commands
      relative:  error, extensions, fancyopts, hg, hook, util
   mercurial/fileset.py mixed imports
      stdlib:    parser
      relative:  error, merge, util
   mercurial/revset.py mixed imports
      stdlib:    parser
      relative:  discovery, error, hbisect, phases, util
   mercurial/templater.py mixed imports
      stdlib:    parser
      relative:  config, error, templatefilters, util
   mercurial/ui.py mixed imports
      stdlib:    formatter
      relative:  config, error, scmutil, util
   Import cycle: mercurial.repoview -> mercurial.revset -> mercurial.repoview
   Import cycle: mercurial.fileset -> mercurial.merge -> mercurial.subrepo -> mercurial.match -> mercurial.fileset
   Import cycle: mercurial.cmdutil -> mercurial.context -> mercurial.subrepo -> mercurial.cmdutil -> mercurial.cmdutil
   Import cycle: mercurial.filemerge -> mercurial.match -> mercurial.fileset -> mercurial.merge -> mercurial.filemerge