When parsing attribute patterns, we will eventually unescape the
parsed pattern. This is required because we require custom
escapes for whitespace characters, as normally they are used to
terminate the current pattern. Thing is, we don't only unescape
those whitespace characters, but in fact all escaped sequences.
So for example if the pattern was "\*", we unescape that to "*".
As this is directly passed to fnmatch(3) later, fnmatch would
treat it as a simple glob matching all files where it should
instead only match a file with name "*".
Fix the issue by unescaping spaces, only. Add a bunch of tests to
exercise escape parsing.
