Quote the eval argument, so bash-quoted arguments survive

[fowlie]

eval $1 in __bass.py is unquoted, so bash performs word splitting and pathname
expansion on the command string before eval parses it. Quoting that is correct for
bash therefore does not survive the round trip.

$ bass printf "'[%s]\n'" "'a  b'"
[a b]                       # one space; the argument was quoted for bash

$ bass printf "'[%s]\n'" "'*'"
[LICENSE]
[Makefile]
[README.md]
[functions]
[test]                      # a quoted glob, expanded against the cwd

With eval "$1" the string reaches eval intact and both behave as the quoting asks:
[a b], and [*].

This is #105. It shows up whenever a caller quotes properly on the fish side — which is
what a fish wrapper around bass has to do, since fish strips its own quotes before bass
ever sees the arguments.

What this deliberately does not change

bass's contract is that its arguments form a bash command line, and that stays true:

• bass source ~/.nvm/nvm.sh --no-use ';' nvm use iojs still works — ';' reaches bash
  as a separator, exactly as the README documents.
• An unquoted * is still a glob, because at that point it is shell syntax the caller
  wrote, not data.

The only difference is that quoting is no longer stripped before bash can honour it.

Test

test/test_quoted_arguments.fish asserts both symptoms and is wired into make test. It
fails on the unpatched version (no Success, exit 1) and passes with the change. The four
existing tests still pass.