run-tests: fix whitelist/blacklist with directories on Windows
The file name is resolved with `os.path.relpath()` in the `Test` constructor,
which yields `\` on Windows. That doesn't match the `/` separator when using
MSYS tools to build the list, and it isn't obvious that this is the problem
because directory separators can mostly be used interchangeably. The
`--test-list` argument already seems to be properly handled.
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1