Import sed_contains from file.py in win_file.py

Also fix small inconsistency in the sed escape function
Return True even if no changes in `file.sed` (fixes #4481)

Issue #4481 gives a completely valid use case for sed which results in
the `begin` pattern always being present.  `sed` should not return False
in this case.
Make module function `file.sed` return the `cmd.run_all` dict
Use the options var we defined earlier, fix win_file.contains
Check file.sed return code, only return False if it errored
Merge pull request #4498 from basepi/sed4481

Don't return False on `file.sed` if no changes, check retcode instead