Revert simplistic fix pending revisit of Mozilla integration attempt.
4 test "$(subst a,b,value)" = "vblue"
5 test "${subst a,b,va)lue}" = "vb)lue"
6 test "$(subst /,\,ab/c)" = "ab\c"
7 test '$(subst a,b,\\#)' = '\\#'
8 test "$( subst a,b,value)" = ""
9 test "$(Subst a,b,value)" = ""
10 test "$(unknown var)" = "uval"