Double expansions of variables had the following issues:
* `"$$foo"` threw an error no matter what the value of `$foo` was.
* `set -l foo ''; echo $$foo` threw an error because of the expansion of
`$foo` to `''`.
With this change, double expansion always works properly. When
double-expanding a multi-valued variable, in a double-quoted string the
first word of the inner expansion is used for the outer expansion, and
outside of a quoted string every word is used for the double-expansion
in each of the arguments.
> set -l foo bar baz
> set -l bar one two
> set -l baz three four
> echo "$$foo"
one two baz
> echo $$foo
one two three four
Enhance the `read` builtin to support creating an array with the --array
flag. With --array, only a single variable name is allowed and the
entire input is tokenized and placed into that variable as an array.
Also add custom behavior if IFS is empty or unset. In that event, split
the input on every character, instead of the previous behavior of doing
no splitting at all.
This commit makes fish_parse_opt stop at first non-option argument,
which expected as fish script name and pass the remaining argument to
that script. I also updated the test cases.
