rw_shell_expand() doesn't interpret quotes

Quoting from this post:

In the shell, spaces that are otherwise treated as separators can
be either escaped or quoted to have them interpreted as ordinary
characters. The rw_xxx_expand() functions let me escape spaces
but they don't seem to like quoting. For example, the shell expands
the following three strings to the same result:

     "a{b\ c,d}"    ==> "ab c ad"
     "a{b' 'c,d}"
     "a{b" "c,d}"

but rw_brace_expand() fails on the last two. It should work the
same as the shell.

In the change below I've enhanced the 0.braceexpand.cpp test
to exercise a number of (passing) test cases including plan as well
as escaped whitespace:

http://svn.apache.org/viewvc?rev=642790&view=rev

I think the same test cases should be added for quoted whitespace.