Add some tests to detect the presence of a bug in sh reported by
Martijn Dekker (private e-mail.)  Variable expansions that are
double quoted result in literal characters (nver pattern matching
meta chars.)  This includes '\' (that one was the bug.)
[On the other hand, a variable in a case pattern expansion that is
unquoted, produces a pattern, and in that the \ character can be
used to excape other pattern meta-chars (and itself.]

This addition will cause the case_matching test case to fail (two
of the newly added sub-tests fail) until fixes to /bin/sh are made.
(That is comiung soon, the code exists already.)

(kre)