Make sure test lists with "foreign" separator still cause the
correct discovery/usage.

Signed-off-by: Mats Wichmann <mats@linux.com>

In the past, there have been some mismatches between how tests are
specified and how they are found.  testlist files, excludelist files
and command-line specifications should be agnostic to operating system
conventions. For example, typing "runtest.py foo/bar" on windows
will produce paths like foo/bar\test.py, which is hard to match and
painful to read, it should obviously match discovered foo\bar\test.py.
Test information should be output using the native path separator for
consistency.

Using pathlib lets these be normalized - stored in a common format and
output in the expected format.

Adding this normalization of course broke some tests, which either
intentionally or through omission expected some portion of a path to
be UNIX-style. Specifically these five:

    test\runtest\baseline\fail.py
    test\runtest\baseline\no_result.py
    test\runtest\simple\fail.py
    test\runtest\simple\no_result.py
    test\runtest\simple\pass.py
    test\runtest\testargv.py

This was fixed and a general cleanup/reformat performed on the
runtest tests.

Signed-off-by: Mats Wichmann <mats@linux.com>

Some nearby things in Main.py as well:
- docstrings polished a bit, minor linting
- move the list of predefined SConstruct file names into a constant
  defined at the top of the file, so it's a little less hidden,
  in the unlikely case of future changes.

Manpage text and example revised a bit.

Signed-off-by: Mats Wichmann <mats@linux.com>

Signed-off-by: Mats Wichmann <mats@linux.com>

MergeFlags has a post-processing step if the *unique* flag evaluates True
which loops through and removes the duplicates. This step uses slicing
(for v in orig[::-1]), which fails if the item being cleaned is a deque -
which CPPDEFINES can now be. It would also cause the deque to be
replaced with a list.  Detect this case and handle separately.

Note the same post-processing step assures each modified object will
be replaced - Override(parse_flags=xxx) silently counted on this so
it does not end up sharing variables with the overridden env. This
situation remains, and is accounted for by the patch.

Unit test and e2e tests are extended to check that MergeFlags can now
add correctly, and that Override leaves the variables independent,
not shared.

Fixes #4231

Signed-off-by: Mats Wichmann <mats@linux.com>

Signed-off-by: Mats Wichmann <mats@linux.com>

Proposed addition of code to cause stub qt to fail,
and test/import.py to detect this situation.
Unfortunately, it doesn't seem to work... needs adjustment.

Doc updates to record rename version.

Signed-off-by: Mats Wichmann <mats@linux.com>