support escape character for white space in running single test case with option -t or -f

in case of having test cases like `exports['test case']`

I am not able to use either `-f` or `-t`
`nodeunit tc.js -t 'test case'` as space is delimiter and it looks for folder instead
`Error: ENOENT, stat '/Users/xxxxx/test/case'`

Please let me know if there is existing options to escape , and please support `\` as espace char white space. quite trivial but I think helpful.Thanks.

Start with the nodeunit command-line entry point used by `nodeunit tc.js -t 'test case'` and trace how the `-t` and `-f` arguments are parsed. Reproduce the reported whitespace failure, then verify that an escaped space selects `exports['test case']` rather than being treated as a path delimiter.

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