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.

tests/run-tests.py

@@ -361,7 +361,8 b' def parselistfiles(files, listtype, warn'
         for line in f.readlines():
             line = line.split(b'#', 1)[0].strip()
             if line:
-                entries[line] = filename
+                # Ensure path entries are compatible with os.path.relpath()
+                entries[os.path.normpath(line)] = filename
 
         f.close()
     return entries

tests/test-run-tests.t

@@ -1116,15 +1116,17 b' Skips with xml'
   </testsuite>
 
 Missing skips or blacklisted skips don't count as executed:
-  $ echo test-failure.t > blacklist
+  $ mkdir tests
+  $ echo tests/test-failure.t > blacklist
+  $ cp test-failure.t tests
   $ rt --blacklist=blacklist --json\
-  >   test-failure.t test-bogus.t
+  >   tests/test-failure.t tests/test-bogus.t
   running 2 tests using 1 parallel processes 
   ss
   Skipped test-bogus.t: Doesn't exist
   Skipped test-failure.t: blacklisted
   # Ran 0 tests, 2 skipped, 0 failed.
-  $ cat report.json
+  $ cat tests/report.json
   testreport ={
       "test-bogus.t": {
           "result": "skip"
@@ -1133,6 +1135,8 b" Missing skips or blacklisted skips don't"
           "result": "skip"
       }
   } (no-eol)
+  $ rm -r tests
+  $ echo test-failure.t > blacklist
 
 Whitelist trumps blacklist
   $ echo test-failure.t > whitelist